8.40cm = 0.4m.
50÷(3. 14×0.4)≈40 (weeks)
9.50× 4+3.14× 50 ÷ 2 = 278.5cm = 2.785m.
10. The perimeter of the shaded part is the sum of half the perimeter of the big circle and the perimeter of the small circle.
2× 3.14× (5÷ 2)+3.14× 5 = 31.4 (cm)