1. Compute $\sin 18^{\circ}$ without tables.
1. $\sin \left(18^{\circ} \cdot 2\right)=\cos \left(18^{\circ} \cdot 3\right)=$ $=4 \cos ^{3} 18^{\circ}-3 \cos 18^{\circ}$, but $\sin \left(18^{\circ} \cdot 2\right)=2 \sin 18^{\circ} \cos 18^{\circ}$. $2 \sin 18^{\circ} \cos 18^{\circ}=4 \cos ^{3} 18^{\circ}-$ $3 \cos 18^{\circ}$. From this, $\sin 18^{\circ}=$

$$
=\frac{\sqrt{5}-1}{4}
$$

| Number of children in families |  |  |  | Sum | Product |
| :---: | :---: | :---: | :---: | :---: | :---: |
| $d$ | $c$ | $b$ | $a$ |  |  |
| 2  2  2  2  2  2  2  1 | 3  3  3  3  3  3  4  2 | 4  4  4  4  5  5  5  3 | 5  6  7  8  6  7  6  4 | 14  15  16  17  16  17  17  10 | 120  144  168  192  180  210  240  24 |
| 1  1 | 4  4 | 5  5  5 | 6  7 | $\dot{16}$  17 | $12 \dot{0}$  140 |