42:36 =

$$\frac{12}{25} : 36 = \frac{12}{25} : \frac{36}{1} = \frac{12}{25} \times \frac{1}{36} = \frac{12 \times 1}{25 \times 36} = \frac{12}{900} = \frac{1}{75}$$.

Ответ: $$\frac{1}{75}$$