Subtracting fractions with unlike denominators

Difficulty Starter · Set 6auu83

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1
56−14=
2
27−18=
3
12−15=
4
23−37=
5
67−12=
6
13−16=
7
45−12=
8
45−12=
9
23−58=
10
45−12=
11
56−14=
12
57−15=
13
58−14=
14
67−23=
15
13−14=
16
57−12=
17
13−17=
18
12−38=
19
34−25=
20
47−15=

What is in this set

The numbers in this set run from 1 to 8.
Every problem in it will have unlike denominators.
20% of them need simplifying at the end.
A careful solution takes 4 written steps on average.
The mistake this set invites most often, in 72% of the problems: the tops were combined and the bottoms were combined; the denominator names the size of the part and never changes when parts are counted.
Answers are a fraction in its lowest terms, written like 3/4.

Drawing 240 problems from this page produced 110 different ones, 46% — so a sheet of 20 will come back to a problem you have seen — there are only so many sensible ones of this kind.

The same skill, harder or easier

We would put this in front of a grade 5 class. That is our judgement, not a standard, and it is printed here so you can disagree with it. Everything else we put in that year.