Question

Machine A working alone can complete a job in 3 1/2 hours. Machine B working alone can do the same job in 4 2/3 hours. How long will it take both machines working together at their respective constant rates to complete the job?A. 1 hr 10 minB. 2hrC. 4hr 5 minD. 7hrE. 8 hr 10 min

Answer 1

B) 2 hours

Explanation:

If machine A complete a job in 3 1/2 hours or 7/2 of an hour

means that in one hour finished 1÷ 7/2 or 2/7

If machine B complete a job in 4 2/3 hours or 14/3 of an hour

means that in one hour finished 1÷ 14/3 or 3/14 of an hour

Then the two machines working together in one hour will make

2/7 + 3/14 = (4 + 3)/ 14

or 7/14 = 1/2

half of the job. Therefore these two machines working together will take two hours