Unit 2
4 marks · NormalAmira draws a circle with a radius of 5 cm.
Calculate the area of the circle. Give your answer correct to 1 decimal place.
Amira increases the radius by 20%. What is the new area of the circle, correct to 1 decimal place?
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 78.5 cm²
(b) 113.1 cm²
Common mistakes: Incorrect formula usage; Using incorrect percentage increase
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correct area formula (πr²) attempted
A1 (a) · 1 mark · Area calculated as 78.5 cm²
M2 (b) · 1 mark · Finds 20% increase in radius and recalculates area
A2 (b) · 1 mark · New area calculated as 113.1 cm² (follow-through)
Worked solution
a) Area = π × r² = π × 5² = π × 25 ≈ 78.5 cm²
b) New radius: 5 + 20% of 5 = 5 + 1 = 6 cm. Area = π × 6² = π × 36 ≈ 113.1 cm²