A number as a product of primes

Difficulty Standard · Set u2s9hk

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1
Write 34 as a product of prime numbers, smallest first, separated by ×.
2
Write 12 as a product of prime numbers, smallest first, separated by ×.
3
Write 135 as a product of prime numbers, smallest first, separated by ×.
4
Write 28 as a product of prime numbers, smallest first, separated by ×.
5
Write 18 as a product of prime numbers, smallest first, separated by ×.
6
Write 63 as a product of prime numbers, smallest first, separated by ×.
7
Write 136 as a product of prime numbers, smallest first, separated by ×.
8
Write 80 as a product of prime numbers, smallest first, separated by ×.
9
Write 93 as a product of prime numbers, smallest first, separated by ×.
10
Write 145 as a product of prime numbers, smallest first, separated by ×.
11
Write 38 as a product of prime numbers, smallest first, separated by ×.
12
Write 68 as a product of prime numbers, smallest first, separated by ×.
13
Write 39 as a product of prime numbers, smallest first, separated by ×.
14
Write 78 as a product of prime numbers, smallest first, separated by ×.
15
Write 87 as a product of prime numbers, smallest first, separated by ×.
16
Write 142 as a product of prime numbers, smallest first, separated by ×.
17
Write 76 as a product of prime numbers, smallest first, separated by ×.
18
Write 142 as a product of prime numbers, smallest first, separated by ×.
19
Write 45 as a product of prime numbers, smallest first, separated by ×.
20
Write 124 as a product of prime numbers, smallest first, separated by ×.

What is in this set

The numbers in this set run from 12 to 150.
95% of them use more than one prime.
A careful solution takes 3 written steps on average.
The mistake this set invites most often, in 48% of the problems: a prime that divides more than once has to appear more than once in the product.
Answers are a short answer exactly as the problem asks for it.

Drawing 240 problems from this page produced 93 different ones, 39% — 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 6 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.