Subtracting with mixed numerals: borrowing
The tutor shows a method of subtracting mixed numerals.
Imagine facing a question such as the following:
5 1/7 – 2 2/3
A convenient approach is “number minus number, fraction minus fraction”:
5-2 + 1/7-2/3
The trouble here is, 1/7 < 2/3. A way out is to borrow one whole from the 5:
4-2 + 1 1/7-2/3
Next, we convert 1 1/7 to an improper fraction (see my post here for how to do so).
2 + 8/7-2/3
To subtract the fractions, we need common demoninators:
2 + (8×3)/(7×3) – (2×7)/(3×7)
which gives
2 + 24/21 – 14/21
With common denominators, we subtract the fractions:
2 10/21
Another way to subtract mixed numerals is to put them in improper fraction form at the beginning. In a future post I’ll comment on the advantages and disadvantages of that method versus the one discussed here.
HTH:)
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.
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