A lamppost casts a shadow that is 18 feet long. At the same time of day, Jenny casts a shadow that is 4.2 feet long. Jenny is 5.3 feet tall. Find the height of the lamppost to the nearest foot. Show all of your work.

Question

A lamppost casts a shadow that is 18 feet long.  At the same time of day, Jenny casts a shadow that is 4.2 feet long.  Jenny is 5.3 feet tall.  Find the height of the lamppost to the nearest foot.  Show all of your work.

wolf1728 · Answer

This is a simple proportion.
Jenny height 5.3 / shadow 4.2
So her height is 5.3/4.2 times her shadow length
or a ratio of 1.2619047619
So the lamp post with an 18 foot shadow has a height of
18 * 1.2619047619 = 22.7142857143 feet
Rounded to the nearest foot = 23 feet

jamanorthi · Answer

oh thanks 
but why did multiply 18*1.2619047619?

jdoe0001 · Answer

|dw:1392511194380:dw|

wolf1728 · Answer

because that is the ratio at that time of day for height / shadow.

jamanorthi · Answer

oh okay thanks i got it

wolf1728 · Answer

okay