Question

Raju can finish a piece of work in 20 days. He worked at it for 5 days and then Jakob alone finished the remaining work in 15 days. In how many days can both finish it together?
1. 12 days
2. 10 days
3. 20 days
4. 16 days

Answer 1

Correct Answer - Option 2 : 10 days

Given :

Raju can finish a piece of work in 20 days

Raju worked for 5 days

Jakob finished the remaining work in 15 days

Concept used :

The efficiency of work = 1/(number of days to finish work)

Solution :

Raju worked for 5 days

So, the remaining work will be finished in 15 days by Raju

Jakob can finish the same piece of work in 20 days

The efficiency of Raju = The efficiency of Jakob

One day work of Raju = 1/20

One day work of Jakob = 1/20

One day work working together = (1/20) + (1/20)

⇒ One day work working together = (1 + 1)/20

⇒ One day work working together = 2/20

⇒ One day work working together = 1/10

∴  The number of days they both can finish work together is 10 days.