Mary was working in a chemistry lab with a mixture of chemicals that was 90% water and weighed 20 pounds. After returning to the lab from a weekend break, she calculated the mixture was now 50% water. How much does the mixture now weigh? For purposes of this puzzle, assume the non-water part of the mixture was not affected by evaporation.

Look Manoj...I dnt know whether u hve studied chemistry ever..bt i was a good student of chemistry!! Question says mixture has 90% of water and it weighs 20 pounds...so cnt be possible dat mixture has 90 % of water as volume and mixture weighs 20 pounds...and den later mixture has 50% of water as volume and now he is asking weight of mixture!!

There is nowhere written in question that 100 gm of mixture has 90 gm of water ( 90 % ) like u assumed!! There can b another deduction like mixture is 100 ml and 90 ml is water ( still 90 %) !! wt do u think now?

"Question says mixture has 90% of water and it weighs 20 pounds...so cnt be possible dat mixture has 90 % of water as volume and mixture weighs 20 pounds..." - From Your post

In the question can u tell me the way how u assumed as Volume... Imagine the same way i assumed as weight. But still Volume is a possibility but it will not give u the answer. If u assume it as weight then u will get the answer. I have studied chemistry very well and i know where to use that too.

And the question is "How much the mixture weigh now??" If u want then prove me by assuming the 90% of water as volume and find the weight.

Yes..we can find it..We know the density of water.
Suppose the density of water is d (pounds/ml)
Suppose mixture is 100 ml...90 ml water and 10 ml of other substance.
90 ml water weighs 90d.
weight of 10 ml of other substance = 20 -90d.
weight of 10 ml of water = 10d.

in new mixture there is 10 ml of water and 10 ml of other substance.
i.e 20- 90d + 10d = 20 - 80d

Density of water is approx 1 gm/cm^3
Convert it into pound / ml and u will get the solution.
Got it???

Suppose the density of water is d (pounds/ml) Density of water is not 1 pound per 1 ml.
90 ml of water weighs 90d is wrong. (how u assumes 90ml = 90(pounds/ml))

weight of 10 ml of other substance = 20 -90d is also wrong (20 in pounds and 90 in pounds/ml) because the density of other substance is different from the water that we dont know...

If 1 ml weighs d pounds ...so 90 ml will weigh 90d pounds( improve ur basics)
Density of water is 1 gm/cm^3, so we can convet it into pounds / ml
unit of 90d is pounds not pounds/ml. I think ur basics are not clear.
and then wight of 10 ml of other substance has to be 20 -90d.

There cant be a relation MAnoj...u hve assumed the ratio by weight and i hve assumed ratio by volume. In these type of questions there should be explicit mention of the type of ratio.
In volume ratio..density has a role to play.

Hello! Does anyone hear me? I was amazed by how many riddle sites would have the wrong answer of 12 lbs. So your close to showing this answer is wrong. I would like some help in showing where they are going wrong.

if answer is 12lbs then we have
20-80d=12 and so d=.1 lbs/ml of water.
as you pointed out this it not the density of water (which is equal to 0.002205 pounds/ ml precisely.) so twelve is wrong but how did they get twelve?