As a punishment for something naughty that we did, my little brother and I have to whitewash both sides of a fence. We start at the same time, and we each work at a constant rate.
If we each whitewash one side, I'll finish in 2 hours and my brother will finish in 4 hours. But I'm a nice kid, so after I finish my side, I go around to the other side and help my brother finish his side. From the time I start helping him, how many minutes does it take us to finish the job?
+128474 When you finish your side, your brother will still have two hours left.
In one hour you can finish 1/2 of a side and your brother can fininsh 1/4 of aside
So...in one hour working together you both can finish 1/2 + 1/4 = 3/4 of a side
Take the reciprocal of this = 4/3
So....it will take 4/3 of an hour = 1hr 20 min = 80 min to finish once you start helping him
