Hi Marouf.
Question:
Penny is a window washer on a highrise office tower. She works fast  she can complete all the windows on a floor in 20 minutes. There are 20 stories on the building. How many hours does it take her to do the whole building?
Solution:
Start by changing 20 minutes into a fraction of an hour. Then multiply by 20. Then convert that to a mixed fraction.
Cheers,
Stephen La Rocque.
