When solving word problems with proportions, have students create a proportion using “word ratios” before attempting to solve. Sample Problem: The length of the shadow from a tree in Johnny’s yard is 12 feet. Johnny is 5 feet tall and his shadow is 10 feet. What is the height of the tree?
height of tree height of Johnny
__________________ = _________________
length of shadow length of shadow
As in the word ratio above, it is crucial that the same unit of measure be on numerator (top) of each ratio. Hence, height is the word on the top of ratio one and the top or ratio two. The same goes for the denominator. They must always be the same unit. The most commonly made mistake of students is incorrect placement of terms.