Question

Jerry and Kuba are laying a hardwood floor. Working​ alone, Jerry can do the job in 21 hr. If the two of them work​ together, they can complete the job in 12 hr. How long would it take Kuba to lay the floor working​ alone?

Answer 1

Kuba can do the work alone in 28 hours

Explanation:

Please do see the attached files for more explanation.

Answer 2

28 hours

Explanation:

If Jerry alone can do the job in 21 hours, the amount of the job completed per hour is 1/21.

If Jerry and Kuba work together, they can do the job in 12 hours, so the amount of the job completed per hour is 1/12.

If the speed of Jerry is is J and the speed of Kuba is K, we have that:

J = 1/21

J + K = 1/12

1/21 + K = 1/12

4/84 + 84K/84 = 7/84

4 + 84K = 7

84K = 3

K = 3/84 = 1/28

If Kuba can do 1/28 of the job per hour, He can complete the job alone in 28 hours.