Asked by Aiden

Please can someone help me with these last few questions on my homework? You don't have to give an answer because I would very much like to know how to do them?
An open box is formed by cutting squares with side lengths of 3 inches from each corner of a square piece of paper. What is a side length of the original paper if the box has a volume of 675 cubic inches?

21 inches

24 inches

33 inches

36 inches

The weekly cost (C) of growing and selling x acres of flowers is approximated by C = 0.2x2 12x + 240. How many acres of flowers would minimize these costs?

10 acres

20 acres

30 acres

60 acres

Answers

Answered by Steve
If the box originally had side s, then the new box has side s-6, since 3" was cut off each corner. The height of the box is just the 3" that was cut off. So,

s(s-6)^2 = 675
Now, just by inspection, 675 = 3*225 = 3*15^2

So, the box now has sides of 15, and height=3

The original paper was thus 21" on a side.
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