Question

Ann is 5 feet 3 inches tall. To find the height of a lamppost, she measured her shadow to be 8 feet 9 inches and the lamppost’s shadow to be 12 feet. To the nearest inch, what is the height of the lamppost?

Answer 1

Answer: The lamppost is 7 feet 2 inches

Step-by-step explanation: If Ann measured her own height and her shadow, then what she used is a ratio between both measurements. If she can measure the shadow of the lamppost, then she can use the same ratio of her height and it’s shadow to derive the correct measurement of the lamppost.

If Ann’s height was measured as 5 feet 3 inches, and her shadow was 8 feet 9 inches, the ratio between them can be expressed as 3:5.

Reduce both dimensions to the same unit, that is, inches. (Remember 12 inches = 1 foot)

Ratio = 63/105

Reduce to the least fraction

Ratio = 3/5

If the height of the lamppost is H, then

H/144 = 3/5

H = (144 x3)/5

H = 86.4

Therefore the lamppost is approximately 86 inches, that is 7 feet and 2 inches tall.