Lesson 25 Section 2
SUBTRACTING MIXED NUMBERS
Solution. In this example, we may simply subtract the whole numbers and subtract the fractions -- similarly to adding mixed numbers.
But consider the following, in which the fractions are reversed:
To see how to deal with it, consider the following:
We cannot take 40 minutes from 10 minutes -- we need more minutes. To get them, we will break off 1 of the 7 hours, and decompose it into 60 minutes. We then regroup them with 10 minutes.
60 minutes + 10 minutes = 70 minutes:
2 hours from 6 hours is 4 hours. 40 minutes from 70 minutes is 30 minutes.
Solution. We cannot take 11 inches from no inches. To make inches, then, from 8 feet we will take 1 foot -- which is 12 inches:
5 feet from 7 feet is 2 feet. 11 inches from 12 inches is 1 inch.
We can now return to our problem:
We need more fifths. Where will we get them? From 8. We will break off 1 from 8, and decompose it into . (Lesson 21, Example 4.)
We will then add those with the original making a total of .
Actually, the simplest way to do this problem is mentally, by rounding off 1 to 2. (Compare Lesson 7.) That is, add to both numbers.
8 − 1 = 8 − 2 = 6.
Now the mystery, if any, is: How does that numerator get to be 9?
9 is the sum of the original numerator 1 and denominator 8:
7 is the sum of denominator plus numerator: 5 + 2.
The problem then becomes
6 − 1 = 6 − 2 = 4.
Solution. According to the meaning of subtraction,
Compare Lesson 7, Example 2.
Solution. First, we must make the denominators the same:
We cannot take from ; therefore, on taking —1—from 6, the fraction becomes 4-fourths + 2 -fourths = 6-fourths:
Please "turn" the page and do some Problems.
Continue on to the next Lesson.
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