Question

Suresh can do 7/10 of a piece of work in 14 days and with the help of  Karan, he is able to finish the work in 10 days, what time will Karan take to finish the work?

1. 15 days 
2. 5 days 
3. 10 days 
4. 20 days 
5. None of these

Answer 1

Correct Answer - Option 4 : 20 days 

Given

Suresh can do 7/10 of a piece of work in 14 days.

Formula used 

If A and B can do a piece of work in x and y days respectively.  Then,

A’s one day work = 1/x

B’s one day work = 1/y

(A + B)’s one day work = 1/x + 1/y

​Calculation

Suresh can do 7/10 of work in 14 days

Suresh can do 1 work in 14 × 10/7 = 20 days

Suresh ’s one day work = 1/20

(Suresh + Karan)’s one day work = 1/10

Karan’s one day work  = (Suresh + Karan)’s 1 day work – Suresh’s 1 day work

⇒  1/10 – 1/20 = (2-1)/20 = 1/20

∴ Karan will finish the work in 20 days.