Job problem?

Question

Please help:

Dave's team can survey Gilmore cave in 15 hours. If Chris' team helps them they can do the same job together in 9 hours. How long would it take Chris' team to survey the cave without the assistance of Dave's team?

Answer 1

If Dave's team (D) can survey the cave in 15 hours, then in 9 hours they can survey 9/15 of the cave. That means that Chris's team (C) surveyed the other 6/15 of the cave during that 15-hour period.

So if C can do 6/15 in 9 hours, multiply both sides by 15/6 to determine how long it would take C to survey the entire cave:

9 * 15/6 = 22.5 hrs

~ ♥ ~

Answer 2

So, D team surveys the cave at the rate of 1/15 per hour.
D team + C team surveys the whole cave at the rate of 1./9 per hour.
That means that C team added ??? per hour to the survey effort.
Do you get it now?
You have to set it up and solve it yourself.

Answer 3

1/C + 1/D = 1/9
1/C + 1/15 = 1/9
1/C = 1/9 - 1/15
1/C = 5/45 - 3/45 = 2/45
C = 45/2 = 22.5 days