EduGoog

Time & Work

A and B together can reap a field in 30 days. After 20 days work, B is called away and A takes 20 days more to complete the work. B alone could do the whole work in

Option:
A. 48 days
B. 50 days
C. 56 days
D. 60 days
Answer: D . 60 days

Justification:

(A + B)'s 1 day's work = $1/30$ 
(A + B)'s 20 day's work = $20/30 = 2/3$
Remaining work to be done by A = $1 - {2/3} = 1/3$
$1/3$ work is done by A in = $20/1 × 3$ = 60 days.
or A's 1 day's work = $1/60$ 
B's 1 day's work = $1/30 - 1/60 = 1/60$
Hence, B can finish the work in 60 days. 

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