Question

Working alone, Jack can do a puzzle in 5 hours. With his brother's help, the two can do the same puzzle in 2 hours.

How long would it take Jack's brother to do the puzzle alone?

Answer 1

3 hours and 20 minutes

Explanation:

Jack's rate is 1 puzzle for every 5 hours, so his rate per hour is 1/5 of a puzzle per hour.

We need to find the rate of his brother so here is our equation,

1/5 + 1/x = 1/2

1/2 - 1/5 =1/x

3/10 = 1/x

3/ 3x = 3/10

3x=10

x= 3 and 1/3 hours

3 hours and 20 minutes