20% male commuters who travel on routes A and F together are less than 25 years of age and 20% female commuters who travel on the same routes together are less than 25 years of age. What is the respective ratio between the two?

Total commuters who travel on route A = $$\frac{20}{100} \times 4000 = 800$$

Males = $$\frac{3}{8} \times 800 = 300$$

Females = $$800 - 300 = 500$$

Total commuters who travel on route F = $$\frac{12}{100} \times 4000 = 480$$

Males = $$\frac{2}{3} \times 480 = 320$$

Females = $$480 - 320 = 160$$

Male commuters who travel on routes A and F together and are less than 25 years of age

= $$\frac{20}{100} (300 + 320) = 124$$

Female commuters who travel on routes A and F together and are less than 25 years of age

= $$\frac{20}{100} (500 + 160) = 132$$

$$\therefore$$ Required ratio = $$124:132 = 31:33$$