A radius, from the circumference

Difficulty Standard · Set 3h1qq7

Take π as 3.14 and give the answer to two decimal places. The drawings are schematic: work from the lengths marked on them, not from their proportions.

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1
A circle has a circumference of 50.24 mm. What is its radius, in mm?
2
A circle has a circumference of 18.84 mm. What is its radius, in mm?
3
A circle has a circumference of 37.68 m. What is its radius, in m?
4
A circle has a circumference of 25.12 mm. What is its radius, in mm?
5
A circle has a circumference of 56.52 mm. What is its radius, in mm?
6
A circle has a circumference of 87.92 cm. What is its radius, in cm?
7
A circle has a circumference of 18.84 cm. What is its radius, in cm?
8
A circle has a circumference of 43.96 m. What is its radius, in m?
9
A circle has a circumference of 37.68 cm. What is its radius, in cm?
10
A circle has a circumference of 50.24 mm. What is its radius, in mm?
11
A circle has a circumference of 43.96 m. What is its radius, in m?
12
A circle has a circumference of 81.64 cm. What is its radius, in cm?
13
A circle has a circumference of 50.24 cm. What is its radius, in cm?
14
A circle has a circumference of 50.24 mm. What is its radius, in mm?
15
A circle has a circumference of 12.56 mm. What is its radius, in mm?
16
A circle has a circumference of 56.52 cm. What is its radius, in cm?
17
A circle has a circumference of 31.40 m. What is its radius, in m?
18
A circle has a circumference of 12.56 m. What is its radius, in m?
19
A circle has a circumference of 31.40 m. What is its radius, in m?
20
A circle has a circumference of 87.92 m. What is its radius, in m?

What is in this set

The numbers in this set run from 12.56 to 94.2.
Every problem in it will run the formula backwards.
A careful solution takes 2 written steps on average.
The mistake this set invites most often, in 100% of the problems: the circumference was halved.
Answers are a whole number.

Drawing 240 problems from this page produced 42 different ones, 18% — 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 8 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.