The circumference of a circle is 187cm. Calculate its diameter.

Tunapewa $C = 187 \text{ cm}$. Tutatumia $\pi = \frac{22}{7}$.

$$187 = \frac{22}{7} \times d$$

$$d = \frac{187 \times 7}{22}$$ $$d = \frac{1309}{22}$$ $$d = 59.5 \text{ cm}$$

Kipenyo cha duara ni $\boxed{\text{59.5 cm}}$.

3. A wheel has a diameter of 70cm. How many meters will it cover after making 300 revolutions?

Mzingo ni umbali unaofunikwa kwa mzunguko mmoja. Tumia fomula $C = \pi d$. Tutatumia $\pi = \frac{22}{7}$.

$$C = \frac{22}{7} \times 70 \text{ cm}$$ $$C = 22 \times 10 \text{ cm}$$ $$C = 220 \text{ cm}$$

$$\text{Jumla ya umbali} = C \times \text{idadi ya mizunguko}$$ $$\text{Jumla ya umbali} = 220 \text{ cm} \times 300$$ $$\text{Jumla ya umbali} = 66000 \text{ cm}$$

Tunajua kuwa $1 \text{ m} = 100 \text{ cm}$.

$$\text{Jumla ya umbali (mita)} = \frac{66000}{100} \text{ m}$$ $$\text{Jumla ya umbali (mita)} = 660 \text{ m}$$

Gurudumu litafunika umbali wa $\boxed{\text{660 m}}$.

4. A circular field has a radius of 60m. An athlete ran round the field four times. What distance in km did he cover? ($\pi=3.142$)

Mzingo ni umbali wa mzunguko mmoja. Tumia fomula $C = 2 \pi r$.

$$C = 2 \times 3.142 \times 60 \text{ m}$$ $$C = 6.284 \times 60 \text{ m}$$ $$C = 377.04 \text{ m}$$

$$\text{Jumla ya umbali} = C \times 4$$ $$\text{Jumla ya umbali} = 377.04 \text{ m} \times 4$$ $$\text{Jumla ya umbali} = 1508.16 \text{ m}$$

Tunajua kuwa $1 \text{ km} = 1000 \text{ m}$.

$$\text{Jumla ya umbali (km)} = \frac{1508.16}{1000} \text{ km}$$ $$\text{Jumla ya umbali (km)} = 1.50816 \text{ km}$$

Mwanariadha alifunika umbali wa $\boxed{\text{1.50816 km}}$.