Grapes have 80% water (by weight). When kept in the sun to dry, only some of the water evaporates and I get raisins, having 10 % water(by weight). If I need 1kg of raisins, how many kgs of grapes should I dry?

TITA type i.e. Type In The Answer type

In such cases, keep in mind that portion having no water i.e pulp must be equal before and after drying.

4.5 kg

pulp in grapes= dried portion of raisins

Let weight of grapes needed in kgs= x

20% of x = 90% of 1

$\frac{20 x}{100}$ = $\frac{90*1}{100}$

x= 9/2 kgs =4.5kgs