# How much water must be evaporated from 60 kilograms of a 15 salt solution in order to obtain a 40% solution?

Dec 30, 2017

28.5 kg

#### Explanation:

The initial strength of the solution is 15% m/m. [Mass/Mass]

That means, the salt present in the solution is = $60 \cdot \frac{15}{100}$ kg = $9$ kg

The water present = $60 - 9$ kg = $51$ kg

If we evaporate some of the water off the solution, the salt should not change its mass, unless it decomposes or something like that.

Let's assume that we have evaporated $x$ kg of water.

According to the condition,

$\frac{9}{51 - x} \cdot 100 = 40$

$\Rightarrow \frac{900}{51 - x} = 40$

$\Rightarrow 51 - x = \frac{900}{40}$

$\Rightarrow 51 - x = 22.5$

$\Rightarrow x = 28.5$

That means 28.5 kg of water needs to be evaporated.