math
posted by fred .
a man is 6ft tall and he casts a shadow of 5 ft, if a tree casts a 30ft shadow, how tall is the tree?

math 
Ms. Sue
Cross multiply this ratio and solve for x.
5/6 = 30/x 
math 
fred
Ms Sue I'm still stuck

math 
bob
5/6=30/x
You can see that 5 was multiplied by 6 to get 30. In order to keep the fraction the same, you'll also have to multiply the 6 in the denominator by 6 to get 36 as your value for x, which in this case represents the height of the tree in feet. 
math 
Ms. Sue
When you cross multiply, you multiply the two farthest terms for the numerator and the two closest terms for the denominator.
5/6 = 30/x
5x = 6 * 30
5x = 180
x = ? 
math 
fred
X=36

math 
Ms. Sue
Right. The tree is 36 feet tall.
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