Question

The ratio of water to milk in a mixture is 5:7. If 15 ml of water is added to the mixture, how much milk should be added to keep the mixture intact?

• A. 20
• B. 21
• C. 22
• D. 23

Answer 1

The correct option is B 21

Before mixing with water :
The ratio of water to milk = 5 : 7

After mixing with water :
Let there be x ml of milk to be added to the mixture, when 15 ml of water is added.

As the ratio in the milk and water in the mixture remains intact before and after adding water
$\Rightarrow \frac{5}{7}=\frac{5+15}{x+7}\Rightarrow \frac{5}{7}=\frac{20}{x+7}$

By cross-multiplication, we get
$5\times (x+7)=20\times 7$
$\Rightarrow x+7=28$
$\Rightarrow x=21$

$\therefore$ 21 ml of milk should be added to the mixture.