how many hours were spent

Question

Bob finished his English assignment in 3/4

 hours. Then he completed his chemistry assignment in 1/5

 hours. What was the total amount of time Bob spent doing these two assignments?

Answer 1

The common denominator is 20

3/4 = 15/20 hr

1/5 = 4/20 hr

Adding them: 19/20 hr

60 minutes per hour:

English 3/4 = 15/20 = 45/60 --> 45 minutes on English

Chem 1/5=4/20 = 12/60 --> 12 minutes on Chem

Adding them 57/60 --> 57 minutes altogether

Note that 19/20 = 57/60