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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