**12.2.2 Solid Geometry (II), PT3 Focus Practice**

**Question 5:**Sphere below has a surface area of 221.76 cm

^{2}.

Calculate its radius.

$\left(\pi =\frac{22}{7}\right)$

*Solution*:Surface area of sphere = 4π

*r*

^{2}

$\begin{array}{l}4\pi {r}^{2}=221.76\\ 4\times \frac{22}{7}\times {r}^{2}=221.76\\ {r}^{2}=\frac{221.76\times 7}{4\times 22}\\ {r}^{2}=17.64\\ r=\sqrt{17.64}\\ r=4.2\text{cm}\end{array}$

**Question 6:**Diagram below shows a right pyramid with a square base.

Given the height of the pyramid is 4 cm.

Calculate the total surface area, in cm

^{2}, of the right pyramid.

*Solution:*h

^{2}= 3

^{2}+ 4

^{2}

= 9 + 16

= 25

h = √25 = 5 cm

^{2}

Total surface area of the right pyramid

= Base area + 4 (Area of triangle)

= (6 × 6) + 4 × 4 (½ × 6 × 5)

= 36 + 60

= 96 cm

^{2}

**Diagram below shows a prism.**

**Question 7:**

Draw to full scale, the net of the prism on the grid in the answer space. The grid has equal squares with sides of 1 unit.

*Solution:*