Question

M can eat some scoops of ice-cream in 9 hours but with the help of N, the ice-cream gets finished in 5 hours. In how many hours can N alone eat the same number of ice-cream scoops? 

1. 11 hours
2. 12 hours
3. 13.5 hours
4. 11.25 hours

Answer 1

Correct Answer - Option 4 : 11.25 hours

Given:

M can eat some scoops of ice-cream in 9 hours.

M and N together ate the ice-cream in 5 hours.

Concepts used:

1 hour work done by individual = Work/time

Calculation:

1 hour work done by individual = Work/time

⇒ 1 hour work of M = 1/9

M and N together ate the ice-cream in 5 hours.

Let N alone can eat the ice-cream scoops in y hours.

⇒ 1 hour work of N = 1/y

⇒ (1/9) + (1/y) = 1/5

⇒ 1/y = (1/5) – (1/9)

⇒ 1/y = 4/45

⇒ y = 45/4 hours = 11.25 hours

∴ N alone can eat scoops of ice-cream in 11.25 hours.