Adding fractions with the same denominator

Difficulty Standard · Set p7mzct

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1
57+17=
2
15+35=
3
15+25=
4
23+13=
5
78+18=
6
310+110=
7
56+12=
8
712+13=
9
45+25=
10
16+12=
11
59+89=
12
78+58=
13
211+411=
14
56+23=
15
27+57=
16
911+111=
17
16+23=
18
310+15=
19
47+57=
20
59+23=

What is in this set

The numbers in this set run from 1 to 12.
Every problem in it will share a denominator.
A careful solution takes 2 written steps on average.
The mistake this set invites most often, in 100% 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 125 different ones, 52% — 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 4 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.