Lisa, an experienced shipping clerk can fill an order in 9 hours. Felipe a clerk needs 11 hours to do the same job. Working together how long will it take them to fill the order.

4 hours and 57 minutes.

Step-by-step explanation:

The least common multiple of 9 and 11 is 99.

In 99 hours, Sue could fill 11 orders (99 divided by 11)

Felipe could fill 9 orders (99 divided by 11), making a total of

9 + 11 = 20 orders if they both work.

So for both of them working to fill one order would take:

99 / 20 hours.

To express in hours and minutes:

99 / 20 = 80 / 20 + 19 / 20 = 4 + 3 ⋅ 19 / 3 ⋅ 20 = 4 + 57 / 60

That's 4 hours and 57 minutes, since a sixtieth of an hour is one minute.