Question

A can do a piece of work in 30 days. He works at it for 6 days and then B finishes it in 18 days. In what time can A and B together it ?
A) 14 1/2 days
B) 11 days
C) 13 1/4 days
D) 12 6/7 days

Answer 1

15

Q:

A can do a piece of work in 30 days. He works at it for 6 days and then B finishes it in 18 days. In what time can A and B together it ?

A) 14 1/2 daysB) 11 daysC) 13 1/4 daysD) 12 6/7 days

Answer:   D) 12 6/7 days 

Explanation:

Let 'B' alone can do the work in 'x' days

6/30 + 18/x = 1

=> x = 22.5

 

1/30 + 1/22.5 = 7/90 

=> 90/7 = 12 6/7 days

Answer 2

A's per day work= 1/30 B complete remaining work in 20 days, work done by a in 5 days=(1/30)5=1/6 remaining work= 5/6 done by B in 20 days then B's per day work=(5/6)(1/20)=1/24

work will completed both A & B working together is inverse of (1/30)+(1/24)=40/3