Carcass wrote:
Ten robots painted 3 identical houses in 5 hours, working at a constant rate. How many hours would it take 20 identical robots to paint 12 such houses, working at the same constant rate?
(A) 2.5
(B) 5
(C) 10
(D) 15
(E) 20
One approach is to use some number sense
Given:
10 robots can paint
3 identical houses in
5 hours
This means:
20 robots can paint
6 identical houses in
5 hours (
if we double the number of robots, we double the output)
This means:
20 robots can paint
12 identical houses in
10 hours (
if we double the required output, we must double the time required)
Answer: C