The lowest common denominator

Difficulty Standard · Set 0428wz

For each pair, give the lowest common denominator.

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1
112&49
2
57&15
3
12&59
4
910&311
5
12&710
6
12&47
7
910&17
8
56&13
9
12&49
10
14&56
11
38&711
12
47&19
13
14&35
14
512&14
15
67&58
16
710&511
17
711&34
18
15&12
19
18&34
20
512&58

What is in this set

The numbers in this set run from 1 to 12.
55% of them share no factor at all.
45% of them share a factor.
A careful solution takes 2 written steps on average.
The mistake this set invites most often, in 45% of the problems: 2 × 8 is a common denominator but not the lowest one.
Answers are a whole number.

Drawing 240 problems from this page produced 219 different ones, 91% — so a sheet of 20 is a new sheet almost every time.

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.

Next to this

The reciprocal of a whole number

Numbers 2–9; every one will have a whole number on one side.

Improper fractions to mixed numbers

Numbers 2–59; every one will cross between improper and mixed form.

All of fractions

24 skills in this topic, 71 sets between them.

Printing it

The printed sheet carries no menus and no advertising, and the answer key is on its own page.