Question

the area of a circular ring enclosed between two concentric circles is 286cm Sq.Find the radii of the two circles given that their difference is 7 cm.

Answer 1

Area of outer circle - area of inner circle = 286 sqcm
Pi(r1² - r2²) = 286 sqcm
Pi(r1 - r2) (r1 + r2) = 286
Pi × 7 × (r1 + r2) = 286
r1 + r2 = 286/22= 13

Now by solving 2 equations simultaneously
r1 + r2 = 13
r1 - r2 = 7
You get r1 = 10cm, r2=7cm