Question

A tank can hold 750 litres of water. At present, it is only $20\%$ full. How many litres of water shall I put into the tank, so that it becomes $60\%$ full?

• A. 100 L
• B. 200 L
• C. 300 L
• D. 400 L

Answer 1

The correct option is C 300 L

Whole = 750 litres (capacity of tank)
Suppose, $20\%$ of 750 litres $=x\text{litres}$
And, $60\%$ of 750 litres $=y\text{litres}$
$\frac{x}{750}=\frac{20}{100}\frac{y}{750}=\frac{60}{100}$
$x=\frac{750\times 20}{100}=150\text{litres}$
$y=\frac{750\times 60}{100}=450\text{litres}$

To raise the water level from $20\%$ to $60\%$, we need to add $(y-x)$ litres of water
i.e. 450 - 150 = 300 litres