Question

A can do a piece of work in 50 days, which B alone can do in 40 days. 20 days after A started the work, B joined it, then in how many days the work was completed?
1. 22.75 days
2. 25 days
3. 33.33 days
4. 35 days

Answer 1

Correct Answer - Option 3 : 33.33 days

Given, 

A can di a piece of work = 50 days

B can do it in 40 days after 20 days B join the work 

Calculation 

Let the total work be the LCM of 50 and 40 i.e. 200

The efficiency of A = 200/50 = 4 units/day

The efficiency of B = 200/40 = 5 units/day

'A' work alone for 20 days to perform work = 20 × 4 = 80 units

A and B complete the remaining work in days = (200 - 80)/9 = 40/3

∴ Total time taken = 20 + 40/3 = 100/3 = 33.33 days