Perimeter of a circle is 2 x π x r, directly proportional to radius r. Therefore, the ratio of circumferences C1 / C2 = (2πr1) / (2πr2) = r1 / r2 = 5 / 4, so ratio of radii is 5:4.
The ratio of the perimeters of two circles is 5:4. What is the ratio of their radii?
Share
Let the radii of the two circles be r1 and r2, and their respective perimeters (circumferences) be C1 and C2.
Formula for circumference is:
C = 2 x π x r
Given ratio of perimeters:
C1 / C2 = 5 / 4
Substituting circumference formulas:
(2 x π x r1) / (2 x π x r2) = 5 / 4
Cancelling common factors 2 and π:
r1 / r2 = 5 / 4.
Thus, the ratio of their radii is also 5:4.
For more NCERT Solutions of Class 9 Ganita Manjari Chapter 6 Measuring Space: Perimeter and Area Question Answer (2026-27)
https://www.tiwariacademy.com/ncert-solutions/class-9/maths/ganita-manjari-chapter-6/