| Problem |
Solution |
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1) It takes 4 workers 5 hours to build 6 structures. At this rate, how long will it take 2 workers to
build 9 structures?
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- Compute the total number of hours to do 1 job:
4x5 = 31⁄3 hours/structure
6
- The number of hours to make 9 structures is:
9 x 31⁄3 = 30 hours.
- Divide this by the number of workers = 30/2 =
15 hours
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2) A coat is priced at $155. In January, the style seems popular so the store raises the price by 20%.
Unfortunately, the coat does not sell at that price. In April, the price is reduced by 20%. What is the
price of the coat after this?
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A price raise of 20% is a multiply of the original price by 1.2
A price reduction of 20% is a multiply of the original price by (1 - 0.2) = 0.8
- Coat price after price raise = $155 x 1.2 = $186
- Coat price after 20% reduction = $186 x 0.8 = $148.80
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3) A rectangular box has a surface area of 94 square inches and a volume of 60 cubic inches. A new box is made that is a scaled up version of this original box. The new box has a surface area of 376 square inches. What is the volume of the new box?
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- Assume the box is a cube. Compute the length of a side as the square root of the total surface area / 6
(because there are 6 sides) :
s =
√
94/6 = 3.958 inches (approx)
- Compute the length of a side of the larger cube :
s =
√
376/6 = 7.916 inches (approx)
- Compute the ratio of these side lengths and cube it:
ratio = (7.916/3.958)2 = 23 = 8
- Multiply the original volume by this ratio:
new volume = 60 x 8 = 480 cubic inches
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