vkgmat wrote:

A person can dig a well in 5 hours. He invites 2 person who can work 3/4 as fast and another 2 person who can work 1/5 as fast as he does. If the 5 person team digs the same well, how long will it take for the team to finsh the job ?

A) 1:20

B) 1:30

C) 1:40

D) 1:50

E) 2:10

Guys, can you please explain how to solve this problem ?

1st person can finish 1/5 of the digging in 1 hour

first 2 people can finish digging 2/(5/(3/4)) = 3/10 in 1 hour

second 2 people can finish digging in 2/(5/(1/5)) = 2/25 in 1 hour

Adding them via a common denominator we get up we get:

(1/T) = 10/50 + 15/50 + 4/50 = 29/50

Thus the time to dig the entire well, T is 50/29 = 1 and 21/29 of an hour

This is roughly equal to 1 hour and 40 minutes (21/29 =~ 40/60)

Answer is C