Area of a semicircle

Difficulty Stretch · Set o82otm

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 semicircle has radius 13 m. What is its area, in square m?
2
A semicircle has radius 40 m. What is its area, in square m?
3
A semicircle has radius 3 m. What is its area, in square m?
4
A semicircle has radius 38 mm. What is its area, in square mm?
5
A semicircle has radius 17 m. What is its area, in square m?
6
A semicircle has radius 27 mm. What is its area, in square mm?
7
A semicircle has radius 7 mm. What is its area, in square mm?
8
A semicircle has radius 10 cm. What is its area, in square cm?
9
A semicircle has radius 38 mm. What is its area, in square mm?
10
A semicircle has radius 20 mm. What is its area, in square mm?
11
A semicircle has radius 38 m. What is its area, in square m?
12
A semicircle has radius 25 m. What is its area, in square m?
13
A semicircle has radius 2 mm. What is its area, in square mm?
14
A semicircle has radius 11 m. What is its area, in square m?
15
A semicircle has radius 27 cm. What is its area, in square cm?
16
A semicircle has radius 25 cm. What is its area, in square cm?
17
A semicircle has radius 23 cm. What is its area, in square cm?
18
A semicircle has radius 31 mm. What is its area, in square mm?
19
A semicircle has radius 33 mm. What is its area, in square mm?
20
A semicircle has radius 8 mm. What is its area, in square mm?

What is in this set

The numbers in this set run from 2 to 40.
A careful solution takes 3 written steps on average.
The mistake this set invites most often, in 100% of the problems: the halving was left out; a semicircle is half of the circle it comes from.
Answers are a decimal.

Drawing 240 problems from this page produced 100 different ones, 42% — 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.