If a maximum of 25 grams of salt dissolves in 100 grams of w

Question

If a maximum of 25 grams of salt dissolves in 100 grams of water and any more salt, if added, remains undissolved and a sediment falls at the bottom. Now, water is evaporated from 1 kilogram of a 4% solution at the rate of 28 grams per hour. After how long would the salt start sedimenting?

A)35 hours
B)30 hours
C)31 hours
D)23 hours
E)none of these

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A)35 hours 
B)30 hours 
C)31 hours 
D)23 hours 
E)none of these

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komalbanka · Answer

Hello,
Are you sure the answer is E?

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Wasif007 · Answer

In my book the answer is e but i think the answer is wrong.....i dont understand how come the answer is e

komalbanka · Answer

According to me, the answer should be B.

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Render · Answer

In other words, the question asks "how much time does it take for the maximum of 250 grams (25 grams of salt per 100 grams of water = 250 grams of salt per 1000 grams of water) to dissolve in a 4% solution of water (i.e. there is only 40 grams of salt there, while the maximum is 250 grams)". Since you don't have the speed at which the salt dissolves, there is not enough info.

The speed at which the water evaporates is simply irrelevant.

Upd: actually, I was wrong: since the salt starts sedimenting at the ratio of salt to water of  1/4  (25 gram/100 gram), we need to find the time period after which the ratio of our existing solution will equal to 1/4. Since the solution contains 40 gr of salt, (4% of 1kg), the least amount of water required for the salt to dissolve is  40*4=160 .

Now, to find out the amount of time required for our 960 gr of water (1000 gr of water - 40 gr of salt) to be equal to 160 gr, we do the following:

(960-160)/28 ≈ 28 , but less than 28 hours.

It doesn't mention the word "approximately" in the question, so I'd choose  5) - none of these

medugar26 · Answer

25gm in 100 gm water

1 gm = 100/25 
 
and  40 gm  =  40* (100/25) = 160 gm

Water is evaporated at 28 gm per hour.
Given 1 litre water with 40 gm salt and thus it will start sedimenting when the ratio of water: salt falls below 4:1
i.e., when the water remaining is less than 160 ml

We can either form an equation like 1000-28n >= 160 and get n<=30
or just check given options and relate it with 28 gm/hr rate to identify that

Till the number of hours is less than equal to 30, it won't start sedimenting and thus it would start sedimenting from the next hour when the water would go below 160 ml

Therefore, the answer is  31 hours , which is the hour in which the sedimentation first begins to happen.

If a maximum of 25 grams of salt dissolves in 100 grams of w

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If a maximum of 25 grams of salt dissolves in 100 grams of w

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

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Perfect 805 Score Debrief by Julia

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