Question

A can do 1 / 5 of a job in 10 days, B can do 1 / 3 rd of the job in 25 days. In how many days can they do half of the job working together?
1. 30
2. 45
3. 15
4. 20

Answer 1

Correct Answer - Option 3 : 15

Given :

A can do 1/5th of work in 10 days

B can do 1/3rd of work in 25 days 

Calculations :

Time taken by A to complete the work = 10 × 5 

⇒ 50 days 

Time taken by B to complete the work = 25 × 3 

⇒ 75 days 

Now, 

Total work = LCM of 50 and 75 

⇒ 150 units 

A per day work = 150/50 = 3 units 

B per day work = 150/75 = 2 units 

Time taken by A and B to complete half work = 75/5          (Half work = 150/2 = 75 units)

⇒ 15 days 

∴ time taken by A and B to complete half the work is 15 days