Question

A tap can fill a tank of $500litres$ in $3hours30minutes$. In how much time will it fill $one-fifth$ of the tank?

Answer 1

Step 1. One-fifth of $500litres$ of tank $=\frac{1}{5}x500=100litres$
Step 2. Time taken by the tap o fill $500litres$ $=3hours30min=3.5hours[30min=0.5hour]$

Therefore time taken by the tap to fill $1litres$ $=\frac{3.5}{500}hours$
Step 3. Time taken by the tap to fill $100litres$ $=\frac{3.5}{500}x100$

$$\begin{gathered} =\frac{3.5}{5} \\ =0.7hour \\ =0.7x60[As1hour=60min] \\ =42minutes \end{gathered}$$

Hence time taken by tap to fill $one-fifth$ of the tank is $42minutes$