Correct Answer - Option 4 : 45 days
Given:
No. of days required by A and B together = 30 days
Concept used:
Total work = No. of days × Efficiency of work
Calculation:
Let the whole work be 1.
⇒ (A + B) × 30 = 1
1 day efficiency of A and B together = 1/30
20 days work of A and B together = 20/30 = 2/3
Remaining work = 1 – 2/3 = 1/3
15 days work of A = 1/3
1 day work of A = 1/45
45 days work of A = 1
∴ A alone can do the entire work in 45 days.