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

The correct answer is: 7.2 hours

Let’s say the area of the lawn is A.
Step 1 of 3:
It is given that Mohan takes 9 hours to mow a lawn of area A.
Area of lawn mowed by Mohan in one hour = 
or we can say that the area that can be mowed by Mohan in one hour is .
Step 2 of 3:
Let’s say that Sohan can mow an area x in one hour. It is given that Mohan and Sohan together mowed the lawn in 4 hours.
Area mowed by Mohan in 4 hours = 4 =  = 
Area mowed by Sohan in 4 hours = 4  x = 4x
Now, Area mowed by Mohan in 4 hours + Area mowed by Sohan in 4 hours = A
+ 4x = A
x = 
Step 3 of 3:
So, Sohan can mow an area of  in one hour.
Time taken by Sohan to mow the whole lawn =  hours
Final Answer:
Hence, the time taken by Sohan to mow the lawn if he works alone is 7.2 hours