CK-12 Geometry Concepts

7.5. Indirect Measurement http://www.ck12.org

58 in

x f t

=

66 in

125 f t

−→ 58 ( 125 ) = 66 (x)

7250 = 66 x

x≈ 109. 85 f t

Example B

Cameron is 5 ft tall and casts a 12 ft shadow. At the same time of day, a nearby building casts a 78 ft shadow. How
tall is the building?

To solve, set up a proportion that compares height to shadow length for Cameron and the building. Then solve the
equation to find the height of the building. Letxrepresent the height of the building.

5 f t

12 f t

=

x

78 f t

12 x= 390

x= 32. 5 f t

The building is 32.5 feet tall.

Example C

The Empire State Building is 1250 ft. tall. At 3:00, Pablo stands next to the building and has an 8 ft. shadow. If he
is 6 ft tall, how long is the Empire State Building’s shadow at 3:00?

Similar to Example B, solve by setting up a proportion that compares height to shadow length. Then solve the
equation to find the length of the shadow. Letxrepresent the length of the shadow.

6 f t

8 f t

=

1250 f t

x

6 x= 10000

x= 1666. 67 f t

The shadow is approximately 1666.67 feet long.

Watch this video for help with the Examples above.

MEDIA

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CK-12 Foundation: Chapter7IndirectMeasurementB