SOLUTION: To find out how wide a certain river is, a pole 20 feet hight is set straight up on one of the banks. Another pole 4 feet long is also set straight up, on the same side, some dista

Question 81407: To find out how wide a certain river is, a pole 20 feet hight is set straight up on one of the banks. Another pole 4 feet long is also set straight up, on the same side, some distance away from the embankment. The observer waits until the shadow of the 20-foot-pole just reaches the other side of the river. At this time he measures the length of the shadow of the 4-foot pole and finds it to be 34 feet. Use this information to determine the width of the river. Show a set-up, equation, solve the equation, and answer the question.
I'm confused with what I'm suppose to do with this problem. Can anyone please help me?
Answer by scott8148(6628) (Show Source): You can put this solution on YOUR website!
the length of the shadow is proportional to the height of the pole ... the ratio of pole to shadow is constant regardless of pole height ... a pole twice as high will cast a shadow twice as long, etc.

this means that 4 is to 34 as 20 is to x ... ... cross multiplying gives 4x=20*34

4x=680 so x=170
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