Question

A gift bag is shaped like a rectangular prism and has a volume of 1152 cubic inches. The width of the bag is w, the length is 2w+4, and the height of the bag is 18-w (which is greater than the width). What are the dimensions of the bag?

Answer 1

1. You must use the formula for calculate the volume of a rectangular prism, which is:

 V=(h)(l)(w)

 V: It is the volumen of the rectangular prism (V=1152 inches³).
 h: It is the height of the rectangular prism (h=18-w).
 l:It is the lenght of the rectangular prism (l=2w+4).

 2. When you substitute these calues into the formula, you obtain:

 V=(h)(l)(w)
 1152=(18-w)(2w+4)(w)
 (18-w)(2w+4)(w)-1152=0

 3. Then, you should mutiply them:

 36w²-2w³+72w-4w²-1152=0
 32w²-2w³+72w-1152=0

 4. When you factor, you obtain:

 2(w-16)(w-6)(w+6)

 w1=16
 w2=6
 w3=-6

 5. The problem says that the height is greater than the width, therefore, the widht is:

 w=6 inches

 6. The length is:

 l=2w+4
 l=2(6)+4
 l=16 inches

 7. And the height is:

 h=18-w
 h=18-6
 h=12 inches

 What are the dimensions of the bag?

 The dimensions of the bag are:

 l=16 inches
 h=12 inches
 w=6 inches