Question

Mohan takes $9$ hours to mow large lawn. He and Sohan together can mow it in $4$ hours. How long will Sohan take to mow the lawn if he works alone? ​

Answer 1

Step : Find the time taken by Sohan

Given:
Time taken by Mohan to mow the lawn $=9$ hours
Time taken by Mohan and Sohan to mow the lawn $=4$ hours

So,
Amount of work done by Mohan in $1$ hour $=\frac{1}{9}$
Amount of work done by Mohan and Sohan in $1$ hour $=\frac{1}{4}$

Amount of work done by Sohan in $1$ hour $=\frac{1}{4}-\frac{1}{9}$

$=\frac{9-4}{36}$

$=\frac{5}{36}$

So, time taken by Sohan to mow the lawn $=\frac{1}{\frac{5}{36}}\text{hours}$

$=\frac{36}{5}\text{hours}$

$=7\frac{1}{5}\text{hours}$