Deciding whether a number is prime

Difficulty Starter · Set 3gefvy

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1
Is 19 prime? Answer yes or no.
2
Is 47 prime? Answer yes or no.
3
Is 31 prime? Answer yes or no.
4
Is 42 prime? Answer yes or no.
5
Is 27 prime? Answer yes or no.
6
Is 39 prime? Answer yes or no.
7
Is 32 prime? Answer yes or no.
8
Is 32 prime? Answer yes or no.
9
Is 32 prime? Answer yes or no.
10
Is 18 prime? Answer yes or no.
11
Is 53 prime? Answer yes or no.
12
Is 28 prime? Answer yes or no.
13
Is 44 prime? Answer yes or no.
14
Is 20 prime? Answer yes or no.
15
Is 42 prime? Answer yes or no.
16
Is 59 prime? Answer yes or no.
17
Is 56 prime? Answer yes or no.
18
Is 13 prime? Answer yes or no.
19
Is 57 prime? Answer yes or no.
20
Is 46 prime? Answer yes or no.

What is in this set

The numbers in this set run from 11 to 60.
78% of them are not prime.
23% of them are prime.
A careful solution takes 3.4 written steps on average.
Answers are a short answer exactly as the problem asks for it.

Drawing 240 problems from this page produced 50 different ones, 21% — 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.