solving word problems

Question

One grocery clerk can stock a shelf in 40 min. A second clerk requires 25 min to stock the same shelf. How long would it take to stock the shelf if the two clerks worked together?

Answer 1

Clerk #1 stocks 1/40 of the shelf per minute.

Clerk #2 stocks 1/25 of the shelf per minute.

Working together they stock 1/40 + 1/25 =

25/1000 + 40/1000 =

65/1000 =

13/200

of the shelf per minute.

It will take them 200/13 = 15 min and 24 seconds to stock the shelf working together