Hi mastermin346,

(a)

The radius of the inner circle is r cm.

The radius of the middle circle is 2r cm.

The radius of the outer circle is 3r cm.

The circumferences form an arithmetic progression with a common difference of

(b)

The radius of the inner circle is 4 cm.

The radius of the middle circle is 8 cm.

The radius of the outer circle is 12 cm.

The common difference in the sequence of circumferences is

The common difference in the radius sequence of 4, 8, 12,..... is 4

To find the radius of the 10th circle use

Use this radius of the 10th circle to compute the circumference: