Question

jack and jerry can complete a job together in 4 hours. if jack require 6 hours to do the job alone, how many hours will it take jerry to do the job alone.
A.12
B.10
C.8
D.6
E.4

Answer 1

jack's rate = 1/6
Jerry's rate = 1/x

combined rate = 1/6 + 1/x
= (x+6)/(6x)

given:
1/( (x+6)/(6x) ) = 4
6x/(x+6) = 4
6x = 4x + 24
2x = 24
x = 12

It would take Jerry to work 12 alone to do the job


check:
combined rate = 1/6 + 1/12
= 3/12 = 1/4

time at combined rate = 1/(1/4) = 4

Answer 2

Thanks