$$\frac{1}{4}:\frac{3}{8}:\frac{20}{15}=$$

$$\frac{1}{4}\times\frac{8}{3}\times\frac{15}{20}=$$

$$\frac{8}{4}\times\frac{15}{3}\times\frac{1}{20}=$$

$$2\times5\times\frac{1}{20}=$$

$$\frac{10}{20}=$$

$$\frac{1}{2}$$