Question 769005
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TAKE your pick of these:

1.  TREE'S HEIGHT over TREE'S SHADOW equals WOMAN'S HEIGHT over WOMAN'S SHADOW
2.  TREE'S HEIGHT over WOMAN'S HEIGHT equals TREE'S SHADOW over WOMAN'S SHADOW

or some other ways as long as you pair them up by 'height', or pair them up by
'shadow'.  {But don't get them criss-crossed)

Let TREE's HEIGHT = t.

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A tree casts a shadow 7.5 ft long
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 TREE'S SHADOW = 7.5
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at the same time that 

a woman 5 ft tall
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WOMAN'S HEIGHT = 5 
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casts a shadow 3 ft long.
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WOMAN'S SHADOW = 3


So if you use

1.  TREE'S HEIGHT over TREE'S SHADOW equals WOMAN'S HEIGHT over WOMAN'S SHADOW

 {{{t/7.5}}}{{{""=""}}}{{{5/3}}},  cross-multiply:
 3t = 37.5
  t = 12.5

or if you use

2.  TREE'S HEIGHT over WOMAN'S HEIGHT equals TREE'S SHADOW over WOMAN'S SHADOW


 {{{t/5}}}{{{""=""}}}{{{7.5/3}}}      cross-multiply
 3t = 37.5
  t = 12.5 

Either way, the tree is 12.5 feet tall.    


Edwin</pre>