Answer:
3.9375 hours
Step-by-step explanation:
Working alone it takes mark 7 hours to mop the whole house it takes sue 9 determine to the nearest hundredth of the hour how long it will take then to mop the house together
This is calculated as
1/Time it would take them to work together = 1/ Number of hours Mark mopped + 1/ Number of hours Sue mopped
= 1/T = 1/7 + 1/9
Lowest common denominator = 63
1/T = 9 + 7/63
1/T = 16/63
T = 63/16
T = 3.9375 hours
