Source: Revised GRE PDF 1st Ed. Section 5: Math; #13 (p. 76)

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In the sunshine, an upright pole 12 feet

In the sunshine, an upright pole 12 feet tall is casting a shadow 8 feet long. At the same time, a nearby upright pole is casting a shadow 10 feet long. If the lengths of the shadows are proportional to the heights of the poles, what is the height, in feet, of the taller pole? 10, 12, 14, 15, 18

1 Explanation

2

Gravatar Chris Lele, Magoosh Tutor

Sep 25, 2012 • Comment

Jacqueline Preisler

what does 120 have to do with the problem?

Dec 9, 2018 • Reply

Sam Kinsman, Magoosh Tutor

The 120 comes from cross multiplying (see https://www.mathsisfun.com/algebra/cross-multiply.html).

We have 8/12 = 10/x. We have to multiply the top of the left fraction by the bottom of the right fraction, so that's 8 * x = 8x. And we have to multiply the bottom of the left fraction by the top of the right fraction, to get 12 * 10 = 120. So we have:

8x = 120

Dec 11, 2018 • Reply

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