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Thread: 7 Math problems I just can't do

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    Lightbulb 7 Math problems I just can't do

    Everyday my school hands out a math problem for the students to solve. The one with the highest score till Christmas wins something
    Sadly I didn't hear about this before the 12th, so I hope my fellow students suck at math so I might have a chance.
    New edit everyday, and thanks in advance!

    12th
    When the camel is thirsty, she consists of 84% water.
    After she drinks, she weights 800kg, and the water percentage rises up to 85%.
    How much does she weight when she's thirsty?
    Answer: 750kg
    First answered by
    Solar Virus

    13th
    Which number comes next?
    4, 9, 17, 29, 46, 69...
    Answer: 99
    First answered by
    DeiJaiVui

    14th
    The Adams family have eaten pancakes. There is 1 liter of the liquid pancake mix stuff left. The mother is going to freeze it. The mother knows it takes exactly 5 scoops to fill the box she is putting it in. But she can't find the scoop, so she uses a smaller scoop. This scoop is half the size of the first one that she couldn't find. Both scoops are half-sphere shaped.
    How many scoops would the mother need to fill the box?
    Answer: 40
    First answered by
    Enslaved

    15th
    Normally it would take 15 minutes to fill the bathtub for the Adams family. But this one time they forgot to seal the drain thing. So it took an hour to fill the bathtub now this time.
    So if the bathtub is full, how long would it take to empty the whole bathtub through the drain?
    Answer: 20 minutes
    First answered by
    masterBB

    16th
    We fill half the cone's volume with water, which is upsidedown where height = 1.
    What is the height of the water?
    Answer: The height of the water level is variable to the radius of the cone.
    First answered by
    Enslaved

    17th I didn't understand this one, so I'll just translate what it says.
    We're going to split a circle in as many pieces possible, with 7 straight lines.
    How many pieces can you get?
    Answer: 29
    First answered by
    Turpinator

    18th
    At the local market garden, there's both male and female employees. 1/3 of the employees brings a child each to work everyday they're going to plant trees. Every male employee plants 13 trees, every female plants 10 trees and every child plants 6 trees. A total of 159 planted that day.

    How many female employees are there?
    Last edited by slackeru; 12-18-2012 at 12:18 PM.

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    The questions grammar is a tad off, i cant be bothered to actually do it, but damn that camel being made from 84% water is interesting


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    750 kg.

    The weight of the non-water mass is 120 kg. (800 x .15)
    So, since the non water weight doesn't change (i assume) use that to find the total weight by dividing the 120 kg by the percentage of mass it takes up (120 / .16)
    Last edited by Solar Virus; 12-12-2012 at 08:03 AM. Reason: Didn't read, changed lbs to kg

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    Quote Originally Posted by Solar Virus View Post
    750 kg.

    The weight of the non-water mass is 120 kg. (800 x .15)
    So, since the non water weight doesn't change (i assume) use that to find the total weight by dividing the 120 kg by the percentage of mass it takes up (120 / .16)
    Why do you multiply 800 with .15? Where do you get from 0.15?

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    Quote Originally Posted by bi a op View Post
    Why do you multiply 800 with .15? Where do you get from 0.15?
    The camels weight after drinking is 800kg, which is made up of 85% water and (100-85)%=15% of the camels own weight.
    Solar from RiD.

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    I know this question has already been answered, but here is how I ended up doing it.

    Quote Originally Posted by bi a op View Post
    When the camel is thirsty, she consists of 84% water.
    After she drinks, she weights 800kg, and the water percentage rises up to 85%.
    How much does she weight when she's thirsty?
    The answer to this question is...

    Weight of camel after drink = 800kg with 85% of that weight being water
    Weight of camel before drink = Xkg with 84% of that weight being water

    Assuming all weight gained while drinking came from the water intake, no water was lost through sweat, urination etc... and its mass that isn't water remained unchanged...

    ...we first need to work out the mass that isn't water by finding the percentage that isn't water and multiplying it by the total mass. (using the values from after drinking)

    800kg x (100%-85%) = 800kg x 0.15 = 120kg

    The percentage of mass that isn't water before drinking is (100%-84%) 16%.
    Therefore, since I'm assuming 120kg is constant,
    16% = 120kg in this case.

    Using that information we can work out that 100% = 750kg

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    The question is wrong. This is not math, this is stupid. I can't solve it.

    edit:

    Changing the question and assuming this:

    Weight of camel after drink = 800kg with 85% of that weight being water
    Weight of camel before drink = Xkg with 84% of that weight being water
    the weight will be 792 kg.

    why?

    because:
    amount of weight * water percentage = water weight
    800 kg * 85 % = 680 kg of water

    85% water = 680 kg
    1% water = 8 kg

    the camel weights 1% less so:
    800kg - 8 kg = 792kg
    Last edited by masterBB; 12-12-2012 at 01:46 PM.
    Working on: Tithe Farmer

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    Quote Originally Posted by masterBB View Post
    The question is wrong. This is not math, this is stupid. I can't solve it.

    edit:

    Changing the question and assuming this:



    the weight will be 792 kg.

    why?

    because:
    amount of weight * water percentage = water weight
    800 kg * 85 % = 680 kg of water

    85% water = 680 kg
    1% water = 8 kg

    the camel weights 1% less so:
    800kg - 8 kg = 792kg
    Correct.

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    Quote Originally Posted by masterBB View Post
    The question is wrong. This is not math, this is stupid. I can't solve it.

    edit:

    Changing the question and assuming this:



    the weight will be 792 kg.

    why?

    because:
    amount of weight * water percentage = water weight
    800 kg * 85 % = 680 kg of water

    85% water = 680 kg
    1% water = 8 kg

    the camel weights 1% less so:
    800kg - 8 kg = 792kg
    That's what I got too.
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    Quote Originally Posted by Aqua3 View Post
    Correct.
    Incorrect, because the % of water is not the same when he is thirsty and when he is satisfied.

    The wight without water of the camel is a constant. This wight will not change if his is thirsty or not, while the weight of the water will so its a variable.

    In conclusion you cant take water as a constant of 85% but you can take camel dry weght as a constant of 15% because this will never change.

    so 15% of 800kg = 120kg
    this 120kg will never change because is the camel dry weight (a constant)
    So independly if your camel has 85 or 84 % of water this will be 15 %.
    well i think so hahaha
    you can buy me, my work, my goals, even you can buy my spirit, but Theres something youll never buy. my indomitable thirst of life.

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    ^^^E: Referring to previously made post about 792kg being the answer.

    No this is not correct.
    This would mean that 1% of 800kg is the same as 1% of weight before, which can not be true. Also it means that the camel consists of 100% water. A % change of water content does not mean the same % change of total mass. These two things might be hard to understand, but there is no need to rephrase this question and your answer is not correct.

    You might find a drastic weight change of 50kg (from 750-800) quite hard to believe, but after doing some research like I did you will find that camels can drink A LOT of water in one go in order to survive in the desert for weeks without water!

    http://www.loc.gov/rr/scitech/mysteries/camel.html
    'They drink large amounts of water - up to 20 gallons at a time. This water is stored in the animal's bloodstream.'
    20 gallons converts to 91 litres to the nearest litre!

    Of course litres and kg are not one and the same thing, but 1 litre of water is in fact roughly 1 kg!

    http://en.wikipedia.org/wiki/Litre
    'From 1901 to 1964, the litre was defined as the volume of one kilogram of pure water at 4 °C and 760 millimetres of mercury pressure.'

    So yes, a change of 50kg is feasible. There is no need to change the question around as apart from a few assumptions...
    1.Non-H2O mass of camel is constant throughout
    2.No mass is lost through excretion
    ...and a few others I can't think of right now the question is perfectly fine!
    As crazy as this might seem - the camel gained 50kg in weight.

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    750 is the correct solution.

    Water percentage = weight of water / total weight * 100

    85% = weight of water / 800kg * 100
    weight of water = 680kg
    weight of non-water (800 - 680)= 120kg

    Let x be equal to the camel's total weight at 84% water.
    84 = (x - 120) / x * 100
    x = 750kg

    check:
    Water percentage = weight of water / total weight * 100
    84 = (750 - 120) / 750 * 100
    84=84

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    Quote Originally Posted by Runehack123 View Post
    ^^^E: Referring to previously made post about 792kg being the answer.

    No this is not correct.
    This would mean that 1% of 800kg is the same as 1% of weight before, which can not be true. Also it means that the camel consists of 100% water. A % change of water content does not mean the same % change of total mass. These two things might be hard to understand, but there is no need to rephrase this question and your answer is not correct.
    Nowhere there is stated that percentage is a percentage of mass. Or a percentage of volume. Or maybe even a percentage of smell. Who knows? To make it easy I assumed they meant percentage of mass.

    The mistake I made was taken the 84% of the 800kg, which it was not. Obviously your answer is right. 750 kg

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    Quote Originally Posted by Runehack123 View Post
    ^^^E: Referring to previously made post about 792kg being the answer.

    No this is not correct.
    This would mean that 1% of 800kg is the same as 1% of weight before, which can not be true. Also it means that the camel consists of 100% water. A % change of water content does not mean the same % change of total mass. These two things might be hard to understand, but there is no need to rephrase this question and your answer is not correct.

    You might find a drastic weight change of 50kg (from 750-800) quite hard to believe, but after doing some research like I did you will find that camels can drink A LOT of water in one go in order to survive in the desert for weeks without water!

    http://www.loc.gov/rr/scitech/mysteries/camel.html
    'They drink large amounts of water - up to 20 gallons at a time. This water is stored in the animal's bloodstream.'
    20 gallons converts to 91 litres to the nearest litre!

    Of course litres and kg are not one and the same thing, but 1 litre of water is in fact roughly 1 kg!

    http://en.wikipedia.org/wiki/Litre
    'From 1901 to 1964, the litre was defined as the volume of one kilogram of pure water at 4 °C and 760 millimetres of mercury pressure.'

    So yes, a change of 50kg is feasible. There is no need to change the question around as apart from a few assumptions...
    1.Non-H2O mass of camel is constant throughout
    2.No mass is lost through excretion
    ...and a few others I can't think of right now the question is perfectly fine!
    As crazy as this might seem - the camel gained 50kg in weight.
    Yes, the water isn't a constant variable, however the non-water matter is. By the way, a problem doesn't have to make sense logically for an answer to be correct (ex. The camel jumped to 98% water weight after drinking), I've seen some pretty bizarre problems.

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    Quote Originally Posted by masterBB View Post
    Nowhere there is stated that percentage is a percentage of mass. Or a percentage of volume. Or maybe even a percentage of smell. Who knows? To make it easy I assumed they meant percentage of mass.

    The mistake I made was taken the 84% of the 800kg, which it was not. Obviously your answer is right. 750 kg

    Actually, in the question it states that the % is a percentage of water.
    'When the camel is thirsty, she consists of 84% water.'
    On a chemical level, % of substance means % of substance in moles compared to a total number of moles within a system. Therefore, comparing a mass to a total mass within a system.

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    Please post answer when you find it out in class.
    Been 30 years since i've done math but it seams to me you guys are over analysing this.
    we know camel weights 800kg @ 85% water. Divide 800 by 85 would give you what 1% would be which is 9.4117647058823529411764705882353 or rounded down which would be 9.41
    800 - 9.41 = 790.59kg
    or rounded up to 791kg
    Again been along time for math problems for me so please post school answer when found out.

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    Quote Originally Posted by wyo64 View Post
    Please post answer when you find it out in class.
    Been 30 years since i've done math but it seams to me you guys are over analysing this.
    we know camel weights 800kg @ 85% water. Divide 800 by 85 would give you what 1% would be which is 9.4117647058823529411764705882353 or rounded down which would be 9.41
    800 - 9.41 = 790.59kg
    or rounded up to 791kg
    Again been along time for math problems for me so please post school answer when found out.
    We've already all established that the correct answer is 750kg and it has been discussed in detail by several people now.

    School answer has already been posted several times now!

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    Thanks for your answers! I answered 750kg, let's hope it's correct (ofc it is).
    New one tomorrow. I'll edit the first post.

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    Quote Originally Posted by bi a op View Post
    Thanks for your answers! I answered 750kg, let's hope it's correct (ofc it is).
    New one tomorrow. I'll edit the first post.
    Oh god, I hope it makes more sense.
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    Quote Originally Posted by Runehack123 View Post
    Actually, in the question it states that the % is a percentage of water.
    'When the camel is thirsty, she consists of 84% water.'
    On a chemical level, % of substance means % of substance in moles compared to a total number of moles within a system. Therefore, comparing a mass to a total mass within a system.
    In moles it wouldn't make sense without a very big and complete study of the kind of moles in a camel. Which of course isn't required. Because if the camel exist out of 85% water and 15% lead, the weight of the lead would be a lot higher compared to when it would have existed out of 15% solid helium.
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    Quote Originally Posted by masterBB View Post
    In moles it wouldn't make sense without a very big and complete study of the kind of moles in a camel. Which of course isn't required. Because if the camel exist out of 85% water and 15% lead, the weight of the lead would be a lot higher compared to when it would have existed out of 15% solid helium.
    Yes, that was wrong what I said there sorry.
    It's actually the % mass as you convert the moles into mass first then calculate the percentage.
    That should make more sense!

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    Quote Originally Posted by Runehack123 View Post
    Yes, that was wrong what I said there sorry.
    It's actually the % mass as you convert the moles into mass first then calculate the percentage.
    That should make more sense!
    Moles are not needed period, these are logic question that involve basic algebra :P

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    New problem!

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    5 8 12 17 23

    each interval add the next one

    so the next number would be +30

    69+30 = 99

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