Bunuel
Two boys can mow a lawn in 2 hours thirty minutes. If 3 other boys helped, how long would it take to mow the same lawn with all of them starting at the same time, each working at their independent rate?
(1) All of the boys work at the same rate.
(2) The boys started mowing at 6 a.m.
First Method : Correct
2 boys mow the lawn in 150 min .
Statement 1 : Both boys work at the same rate . Ra = Rb
Amt = 2 Ra * 150 == > Ra = Amt /300 ==>
Amt = 5 Amt /300 * t
t = 60 min = 1 hr .
Bunuel : I have 1 doubt
If the rate is same than Time is also same to do the same work .
Now in this question , why cant I say after reading the first statement , if they worked together than together they take 75 mins. (because their
combined rate is twice their individual rate).
and when 5 of them worked together than they will take 15 mins . (which i think is wrong).