math
posted by selena on .
Math homework help????? please?
heres what it says on the paper. Using proportions, you can calculate the dimensions of objects without having to measure them. solve the problems that follow...
heres the problem
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amy is 5 feet tall and casts a 4foot shadow. the pine tree has an 8 foot shadow. how tall is the pine tree..????
Please help me understand how to do this

Here's the proportion:
Height is to shadow as height is to shadow. Let x represent the unknown  the height of the tree.
5/4 = x/8
Cross multiply:
4x = 40
Solve for x.
x = 40/4
x = 10
The tree is 10 feet tall.