1. The radii of two circles are 19 cm and 9 cm respectively. Find the radius of the circle which has circumference equal to the sum of the circumferences of the two circles.
Solution: Circumference of first circle
= 2 πr = 2π x 19 = 38π cm
Circumference of second circle = 18π cm
Or, 2πr = 56π
Or, 2r = 56
Or, r = 28 cm
Circumference of the largest circle; as per question
= 38π + 18π = 56π cm
Question: 2. The radii of two circles are 8 cm and 6 cm respectively. Find the radius of the circle having area equal to the sum of the areas of the two circles.
Answer:Area of first circle = πr2
= π82 = 64π sq cm
Area of second circle = π62 = 36π sq cm
As per question; area of the largest circle = 64π + 36π
= 100π sq cm
Or, πr2 = 100π
Or, r2 = 100
Or, r = 10 cm
3. The wheels of a car are of diameter 80 cm each. How many complete revolutions does each wheel make in 10 minutes when the car is travelling at a speed of 66 km per hour?
Solution: Distance covered in 10 minutes = (66/60) x 10 = 11 km
Circumference = πd = 80π
Number of revolutions =
= 51.33 sq cm[frontier_mode=””quickpost”]