11.A school has 8 periods a day each of 45 minutes duration. How long would each period be, if the school has 9 periods a day, assuming the number of school hours to be the same?
∴$$x_1y_1 = x_2y_2$$
$$\Rightarrow 8 \times 45 = 9 \times x$$
$$\Rightarrow x = 40\; minutes$$