3. 14×6= 18.84 (m)

2×3. 14×5=3 1.4 (cm)

2.3.77÷3. 14≈ 1.2 (m)

3.66 cm ≡ 0.66 m2000 ÷ (3.14× 0.66×100) ≈10 (minutes)

4.2× 3.14× 20× 30/60 = 62.8cm.

2×3. 14×20×45/60=94.2 cm.

5.2× 3.14×15× 3 = 282.6m.

2×3. 14× 15÷2≈47 (root)

6. Perimeter of (1) square: 2× 2× 4 = 16 (cm)

Circumference: 2× 3. 14× 2 = 12.56 (cm).

(2) The circumference of a circle: 2× 3. 14× 1.5 = 9.4 (cm).

The circumference of a rectangle: (1.5× 5+1.5× 2× 2) = 21(cm).

7.100 ÷ 4×1/2 =12.5 (cm)

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)