Perimeter and arc length. Game on.

Perimeter and arc length is a grade 10 math skill aligned to Common Core standard HSG.C.B.5: derive the fact that the length of the arc intercepted by an angle is proportional to the radius, and derive the formula for the area of a sector. Below are 8 practice questions with answers and step-by-step explanations, drawn from the 15 perimeter and arc length problems our math games drill.

CCSS HSG.C.B.515 questions in the bank
Kickoff

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Warm-upeasy

Find the arc length of a 90°90° arc on a circle with radius 44. Use π=3\pi = 3.

L=90360×2πr=14×2×3×4=6L = \dfrac{90}{360} \times 2 \pi r = \dfrac{1}{4} \times 2 \times 3 \times 4 = 6.

Mid-gameeasy

A triangle has sides 77, 1010, and 1212. What is its perimeter?

P=7+10+12=29P = 7 + 10 + 12 = 29.

Mid-gameeasy

Find the arc length of a 180°180° arc on a circle with radius 55. Use π=3\pi = 3.

L=180360×2πr=12×2×3×5=15L = \dfrac{180}{360} \times 2 \pi r = \dfrac{1}{2} \times 2 \times 3 \times 5 = 15.

Mid-gameeasy

A rectangular garden measures 1515 by 66. How many units of fencing are needed to go all the way around it?

P=2(15+6)=221=42P = 2(15 + 6) = 2 \cdot 21 = 42.

Mid-gameeasy

Find the arc length of a 90°90° arc on a circle with radius 66. Use π=3\pi = 3.

L=90360×2πr=14×2×3×6=9L = \dfrac{90}{360} \times 2 \pi r = \dfrac{1}{4} \times 2 \times 3 \times 6 = 9.

Mid-gameeasy

Find the arc length of a 180°180° arc on a circle with radius 33. Use π=3\pi = 3.

L=180360×2πr=12×2×3×3=9L = \dfrac{180}{360} \times 2 \pi r = \dfrac{1}{2} \times 2 \times 3 \times 3 = 9.

Mid-gameeasy

Find the arc length of a 90°90° arc on a circle with radius 22. Use π=3\pi = 3.

L=90360×2πr=14×2×3×2=3L = \dfrac{90}{360} \times 2 \pi r = \dfrac{1}{4} \times 2 \times 3 \times 2 = 3.

Buzzer beatereasy

A semicircle has radius 1010. Its curved edge has length kπk\pi. What is the value of kk?

Half the circumference is 122π10=10π\dfrac{1}{2} \cdot 2 \pi \cdot 10 = 10\pi, so k=10k = 10.

Overtime

7 more. Played, not assigned.

The rest of the bank lives inside live head-to-head matches — the placement test finds the right starting difficulty.

Drill it inside a game.

The free placement test finds your level, then every match serves perimeter and arc length questions at exactly the right difficulty.