Correct Answer - Option 2 : 20 days
Given:
X can do a piece of work = 25 days
Percentage increase in efficiency (a) = 25%
Calculation:
X’s one day work = 1/25
Y’s one day work = X’s one day’s work × (100 + a)/100
Y’s one day work
⇒ (1/25) × (100 + 25)/100
⇒ (1/25) × 125/100
⇒ 1/20
Y alone takes 20 days.
∴ The number of days taken by Y is 20 days.