Question

Working together, Bill and Tom painted a fence in 8 hours. Last year, Tom painted the fence by himself. The year before, Bill painted it by himself, but took 12 hours less than Tom took. How long did Bill and Tom take, when each was painting alone?

Answer 1

Tom paints the fence in 24 hours and Bill paints the fence in 12

Explanation:

T = 1 fence / x hours

B = 1 fence / x - 12 hours

B + T = 1 fence / 8 hours

( 1 fence / x - 12 hours ) + ( 1 fence / x hours ) = 1 fence / 8 hours

( 1 / x - 12 ) + ( 1 / x ) = 1 / 8

multiply through all the denominators to get:

8x + 8 (x - 12 ) = x( x - 12 )

8x + 8x - 96 = x^2 - 12x

combine like terms to get:

x^2 - 28x + 96 = 0

factor to get:

( x - 4 ) ( x - 24 ) = 0

x = 4, 24

4 won't work, because that would mean Bill would take a negative amount of time to paint the fence by himself, so that means

Tom paints the fence in 24 hours and Bill paints the fence in 12