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.