13. Find the radius of a circle whosecircumference is equal to the sum

1.	13. Find the radius of a circle whosecircumference is equal to the sum of thecircumference of two circles of radii 15 cmNCERT Exemplarand 18 cm
Answer» Let the radius of a circle be r. ∴ Circumference of a circle = 2πr Let the radii of two circles are r and r whose values are 15 cm and 18 cm respectively. i.e. r1 = 15 cm and r2 = 18 cm Now, by given condition, Circumference of circle = Circumference of first circle + Circumference of second circle ⇒ 2πr = 2πr1 + 2πr2 ⇒ r = r1 + r2 ⇒ r = 15 + 18 ∴ r = 33 cm Hence, the required radius of a circle is 33 cm.

13. Find the radius of a circle whosecircumference is equal to the sum of thecircumference of two circles of radii 15 cmNCERT Exemplarand 18 cm

Answer»

Let the radius of a circle be r.

∴ Circumference of a circle = 2πr

Let the radii of two circles are r and r whose values are 15 cm and 18 cm respectively.

i.e. r1 = 15 cm and r2 = 18 cm

Now, by given condition,

Circumference of circle = Circumference of first circle + Circumference of second circle

⇒ 2πr = 2πr1 + 2πr2

⇒ r = r1 + r2

⇒ r = 15 + 18

∴ r = 33 cm

Hence, the required radius of a circle is 33 cm.