Answer: it will take them 3.73 hours working together.
Step-by-step explanation:
It takes Bethany 8 hours to proof a chapter of Hawkes Learning Systems' Statistics book . This means that the rate at which she proofs a chapter per hour is 1/8
it takes Nina 7 hours. This means that the rate at which Nina proofs a chapter per hour is 1/7
If they work together, they would work simultaneously and their individual rates are additive. This means that their combined working rate would be
1/8 + 1/7 = 15/56
Assuming it takes t hours for both of them to proof a chapter working together, the working rate per hour would be 1/t. Therefore,
15/56 = 1/t
t = 56/15
t = 3.73 hours
