Deciding whether a number is prime

Difficulty Stretch · Set 382gd0

Fill in what you can and press Check. Nothing you type is sent anywhere.

1
Is 351 prime? Answer yes or no.
2
Is 131 prime? Answer yes or no.
3
Is 186 prime? Answer yes or no.
4
Is 17 prime? Answer yes or no.
5
Is 120 prime? Answer yes or no.
6
Is 21 prime? Answer yes or no.
7
Is 61 prime? Answer yes or no.
8
Is 360 prime? Answer yes or no.
9
Is 357 prime? Answer yes or no.
10
Is 231 prime? Answer yes or no.
11
Is 169 prime? Answer yes or no.
12
Is 53 prime? Answer yes or no.
13
Is 187 prime? Answer yes or no.
14
Is 330 prime? Answer yes or no.
15
Is 17 prime? Answer yes or no.
16
Is 56 prime? Answer yes or no.
17
Is 93 prime? Answer yes or no.
18
Is 330 prime? Answer yes or no.
19
Is 299 prime? Answer yes or no.
20
Is 27 prime? Answer yes or no.

What is in this set

The numbers in this set run from 12 to 400.
79% of them are not prime.
21% of them are prime.
A careful solution takes 7.1 written steps on average.
Answers are a short answer exactly as the problem asks for it.

Drawing 240 problems from this page produced 181 different ones, 75% — 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

A number as a product of primes

Numbers 14–400; 93% use more than one prime.

Divisibility tests

Numbers 3–9,963; 55% divide exactly.

Reading Roman numerals

Numbers 0–0; 54% use a subtractive pair such as IV or XC.

All of number sense

28 skills in this topic, 75 sets between them.

Printing it

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