Fresh grapes contain 90% by weight while dried grapes

Here is an official explanation how to solve this problem:

Let x kg dry grapes be obtained. Then, solid part in fresh grapes = solid part in dry grapes
0.1*20=0.8x*x
x=2,5

I do not find this explanation an approriate one because something must be wrong with 0.8x*x.

Can somebody suggest an alternative way of solution?
Thanks. My appreciations+KUDOS!!!

another attempt to make this question easier to understand

question is asking what amount of dry grapes will yield mass of 2 kg

or
80 % of what = 2 kg

answer 2.5

10% of 20 kg = 2kg is without water, there is no water at all in these 2 kg but we need weight with 20% of water and 80% without water. Let X be the weight with 20% water. Therefore X will have the same 2 kg without water, that means these 2kg will be 80% of X, therefore:

80% of X = 2kg
=> X = 2.5kg

Posted from my mobile device

Since the grape content will remain the same
For 20 Kg fresh water grapes if water=90%, grape content= 10%
so 10% of 20= 2 Kg
So in the dry grape, grape content = 2kg
Here water: grape content= 20:80= 1:4 so for 2 kg grape content, water= 0.5: 2
Hence total weight= 2.5 Kg

Since,
Dry grapes+Water = Fresh grapes
One can also do this problem by alligating water.
DRY GRAPES(water)______WATER
________20_________________100
________'________90_________'
________10_________________70
Ratio=> 10 : 70 = 1:7
The weight of Dry grapes
= 1/8×20 = 2.5kgs


I hope this method will help to solve such questions quickly.

Thank you!

Posted from my mobile device

Please find solution in the attached image.

20 kg fresh grapes contains 18 kg (90%) water and remaining 2 kg (20-18 kg) pulp.

When grapes is dried, pulp content remains same (2 kg), whereas water gets dried to lets say x kg.

x kg is 20 % of the entire weight (x+2) kg {water + pulp content}

Therefore, x=0.2(x+2). Hence x=0.5 kg.

Weight of dried grapes = 2 kg (pulp) + 0.5 kg (water) = 2.5 Kg

Fresh grapes contain 90% by weight while dried grapes contain 20% water by weight. What is the weight of dry grapes available from 20 kg of fresh grapes?

It's given that fresh grapes contain 90% water by weight , that means non-water content in fresh grapes will be 10% by weight.
Similarly, dried grapes contain 20% water by weight, so we can also say that non-water content in dried grapes will be 80% by weight.


Here we need to find the weight of dry grapes available from 20 kg of fresh grapes.

Assume that weight of dried grapes available would be X.

So, the non- water content of 20 kg of fresh grapes will be equal to non-water content of X kg of dried grapes available from that.

10% of 20 = 80 % of X

X= 10* 20 / 80 = 20/8 = 2.5 kg

Option C is the answer.

Thanks,
Clifin J Francis,
GMAT SME

Pulp from fresh grapes = 10% of 20 = 2 kg
Pulp from dried grapes = 80% of x = 0.8x kg
Thus: 0.8x = 2
=> x = 2.5 kg

Answer C