Tuesday, January 22, 2013

Subtraction Word Problem

The following problem causes confusion for many students who do not take the time to make sense of the problem and/or their answer.

In June your new puppy weighed 10 2/3 pounds and by July the puppy weighed 19 1/5 pounds.  How much weight did the puppy gain?

First makes sense of the problem by substituting easy whole numbers for the mixed numbers.  Let's make 10 2/3 simply 10 pounds and 19 1/5, 20 pounds.  Then you can make sense of the problem.  It only makes sense to subtract 10 from 20 (20 - 10 = n) to find the difference in pounds or the weight gained. Subtracting 20 from 10 (10 - 20 = n) will give you a negative integer which does not make  sense since the puppy did not lose weight from June to July.

Remember, just because a number comes first in a word problem does not mean that it will come first in a number sentence.  It is important that you stop and think about the situation and make sense of it before you begin your computation.

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