A lamppost is 6 feet high and casts an 8 foot shadow. At the same time of day, a flagpole near the lamppost casts a 20 foot shadow. Using the properties of similar triangles, find the height, H, of the flagpole.

Question

Mathematics

Johanna Perry

25 May, 05:55

A lamppost is 6 feet high and casts an 8 foot shadow. At the same time of day, a flagpole near the lamppost casts a 20 foot shadow. Using the properties of similar triangles, find the height, H, of the flagpole.

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Answers (1)

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Rowan Jones · Answer 1

The height is 15 ft.

Step-by-step explanation:

Set up a proportion using the info you have for the lamppost and for the flagpole. Use H for the unknown.

lamppost flagpole

height/shadow = height/shadow

6/8 = H/20

6/8 = H/20

Reduce the left fraction.

3/4 = H/20

Cross multiply.

4H = 3 * 20

4H = 60

H = 15

The height is 15 ft.