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
Actually, the simplest way to do this problem is mentally
The problem then becomes
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.
Again, the simplest way to do this is mentally
(Lesson 21.) The problem then becomes
Solution. According to the meaning of subtraction,
Compare Lesson 7, Example 2.
Solution. First, we must make the denominators the same:
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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