Jon has 3 boards that are each 8 feet long. First he makes 3 identical shelves. Then he uses 18 inches to make a bird house. When finished, he has 25% of the original amount left. How much wood was used for each shelf, in feet?

Guest Jan 17, 2018

#1**+1 **

Jon has 3 boards that are each 8 feet long. First he makes 3 identical shelves. Then he uses 18 inches to make a bird house. When finished, he has 25% of the original amount left. How much wood was used for each shelf, in feet?

3 x 8 =24 feet - That Jon started with.

25% x 24 = 6 feet left.

24 - 6 = 18 feet used to make 3 shelves and a bird house

18 inches / 12 = 1.5 feet used for the bird house.

18 - 1.5 = 16.5 feet used for the 3 shelves

16.5 / 3 = 5.5 feet used for each of the 3 shelves.

Guest Jan 17, 2018

#2**+1 **

Another approach....let x be the length of each shelf and let 18 in =

18/12 ft = 3/2 ft = 1.5 ft

So we have

[ 3* 8 - 1.5 - 3x ] = .25 [ 3*8] simplify

[ 24 - 1.5 - 3x ] = .25 * 24

22.5 - 3x = 8 add 3 to each side, subtract 8 from both sides

22.5 - 8 = 3x

16.5 = 3x divide both sides by 3

5.5 = x ⇒ 5.5 ft = the length of each shelf

CPhill Jan 17, 2018