Answer: 5 days
Step-by-step explanation:
If a project will take Mr A and Mr B 12 days to complete, this means that
1/A + 1/B = 1/12
(A+B)/AB = 1/12
AB/(A+B) = 12
Cross multiply
AB = 12A + 12B .....(1)
Now that both of them work for 4 days. Part of the job completed is
AB/(A+B) = 4
AB = 4A +4B .....(2)
Minus equation 2 from 1
8A + 8B = 0 ..... (3)
The remaining day = 8 days
If Mr A can complete this in 10 days,
The number of days Mr B take to complete this project will be
1/10 + 1/B = 1/8
1/B = 1/8 - 1/10
1/B = (10 + 8)/80
B = 80/18
B = 4.444 days
Approximately 5 days
