A diameter, from the radius

Difficulty Standard · Set qn57tb

The drawings are schematic: work from the lengths marked on them, not from their proportions.

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

1
The circle's radius is 9 mm. What is its diameter, in mm?
2
The circle's radius is 3 m. What is its diameter, in m?
3
The circle's radius is 3 m. What is its diameter, in m?
4
The circle's radius is 4 m. What is its diameter, in m?
5
The circle's radius is 18 m. What is its diameter, in m?
6
The circle's radius is 12 mm. What is its diameter, in mm?
7
The circle's radius is 5 cm. What is its diameter, in cm?
8
The circle's radius is 8 cm. What is its diameter, in cm?
9
The circle's radius is 6 m. What is its diameter, in m?
10
The circle's radius is 8 m. What is its diameter, in m?
11
The circle's radius is 4 m. What is its diameter, in m?
12
The circle's radius is 3 mm. What is its diameter, in mm?
13
The circle's radius is 14 cm. What is its diameter, in cm?
14
The circle's radius is 8 m. What is its diameter, in m?
15
The circle's radius is 20 m. What is its diameter, in m?
16
The circle's radius is 12 mm. What is its diameter, in mm?
17
The circle's radius is 20 m. What is its diameter, in m?
18
The circle's radius is 9 m. What is its diameter, in m?
19
The circle's radius is 10 cm. What is its diameter, in cm?
20
The circle's radius is 5 cm. What is its diameter, in cm?

What is in this set

The numbers in this set run from 2 to 20.
A careful solution takes 1 written step on average.
The mistake this set invites most often, in 100% of the problems: the radius was halved; the diameter is twice it, right across the circle.
Answers are a whole number.

Drawing 240 problems from this page produced 57 different ones, 24% — 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.