Machine a can complete a certain job in x hours. machine b can complete the same job in y hours. if a and b work together at their respective rates to complete the job, which of the following represents the fraction of the job that b will not have to complete because of a's ? a) (x – y)/(x + y)b) x/(y – x)c) (x + y)/(xy)d) y/(x – y)e) y/(x + y)

Step-by-step explanation:

The required answer is the rate at  which Machine A  works when the two machines are combined.

Note: the rate of doing work is express as

Hence we can conclude that Machine A working rate is

and machine B working rate is

When the two machine works together, the effective working rate is

The fraction of the work that Machine B will not have complete because of Machine A help is the total work done by machine A

Hence the fraction of work done by A is expressed as

Hence the fraction of the work that Machine B will not have complete because of Machine A help is the total work done by machine A is

20

step-by-step explanation:

1. d.90

2. e. none of these (80)

3. a. 0

4. b. 6

5. e. none of these (10)

6. a. 5