Solve question no. 3 of page no. 78 from the chapter "Average" of textbook "Shaping Maths AB 5B Part I - Solutions".

1.50 + 1.80 + 2.50 + 2.20 = 8
 

Press $\boxed{\mathrm{C}}$ 1.50 $\boxed{+}$ 1.80 $\boxed{+}$ 2.50 $\boxed{+}$ 2.20 $\boxed{=}$ Display: 8

The total pocket money of the four girls is $8.

$8 $÷$ 4 = $2    $\left(\mathrm{Average}=\frac{\mathrm{Sum} \mathrm{of} \mathrm{the} \mathrm{data}}{\mathrm{Number} \mathrm{of} \mathrm{data}}\right)$

The average amount of pocket money the girls get is $2.