Question

Ajay can do a work in 45 days and Seema can do the same work in 36 days. In how many days will they finish the work together? 
1. 15 days
2. 20 days
3. 25 days
4. 28 days

Answer 1

Correct Answer - Option 2 : 20 days

GIVEN:

Seema's time = 36 days

Ajay's time = 45 days 

FORMULA USED:

Work = efficiency × time

CALCULATON:

 Let total work be 1 unit

Seema's efficiency = 1/36 unit

Ajay's efficiency = 1/45 unit

Efficiency together = 1/36 + 1/45 = 9/180 = 1/20 unit 

∴ time taken to complete = 20 days (efficiency = work/time)

∴ 20 days will be taken

ALTERNATE SOLUTION:

Let total work be 180 (L.C.M 0f 36,45)

Seema's efficiency = 180/36 = 5

Ajay's efficiency = 180/45 = 4

Efficiency together = (5 + 4) =9

Time taken = 180/9 = 20 days

∴ 20 days will be taken