№ 1.
L = 2пr = 2 * 3,14 * 12 = 75,36 см
№ 2.
L = пd = 3,14 * 13 = 40,82 см
№ 3.
r = L / 2п = 63,428 / 2 * 3,14 = 63,428 / 6,28 = 10,1 дм радиус
d = L / п = 63,428 / 3,14 = 20,2 дм диаметр
№ 4.
9 + 2 3/8 = 8 8/8 + 2 3/8 = 10 11/8 = 11 3/8
9 - 2 3/8 = 8 8/8 - 2 3/8 = 6 5/8
2 3/8 - 9 = 19/8 - 72/8 = - 53/8 = - 6 5/8
- 2 3/8 - 9 = - 19/8 - 72/8 = - 91/8 = - 11 3/8
- 2 3/8 + 9 = - 19/8 + 72/8 = 53/8 = 6 5/8
- 9 + 2 3/8 = - 72/8 + 19/8 = - 53/8 = - 6 5/8