Question

A mixture of 40 litres of salt and water contains 70%of salt.how much water must be added to decrease the salt percentage to 40%?

Answer 1

Here is your answer......I have used the shortcut method of mixture and Alligation to solve it.

Answer 2

30 Litres of water to be added

Given:

Volume of Mixture (Salt & water) = 40 litre and mixture contains 70% Salt.

To find:  

The amount of water to be added.

Solution:

Volume of salt in mixture = 70% salt × volume of mixture$=\left(\frac{70}{100}\right) \times 40=28$ litre

and Volume of water in mixture = 40 - 28 = 12 liter

To decrease the salt percent by 40% Let, x water is added.

Then volume of mixture$= 40 + x$ litre

We know that, Volume of salt = 28 litres  

Therefore,  

Salt% in a new mixture $=\frac{28}{40+x} \times 100$

But Now Salt percent in a new mixture decreases to 40%

$\text{Therefore}, \left(\frac{28}{40+x}\right) \times 100=40 \begin{array}{c}\\\\\\\\{2800=40(40+x)} \\ {2800=1600+40 x} \\ {x=30}\end{array}$