Let the radius of the circle be r cm.
Then, its circumference = (2πr) cm
Now, (circumference) – (diameter) = 30 cm … [given]
∴ (2πr – 2r) = 30
By taking 2r common we get,
= 2r (π – 1) = 30
= 2r × ((22/7) – 1) = 30
= 2r × ((22 – 7)/7) = 30
= 2r × (15/7) = 30
= (30/7) r = 30
= r = (30) × (7/30)
= r = 7 cm
Hence, the radius of the circle is 7 cm.