Hint:
Diameter(d)= 2 radius(r)
circumference= 2πr= πd
1. diameter= 19 × 2 = 38 inches
circumference= 3.18(38) = 119 inches (3 s.f.)
Note that I use 3.18 instead of π because the question states to use 3.14 for π.
Likewise, if you are given the diameter, divide it by 2 to find radius. Let's try a question which only gives you the diameter.
4. radius= 22 ÷ 2 = 11cm
circumference= 3.14(22) = 69.1cm (3 s.f.)
