40% of monkeys = 25% of chimpanzees (since \( \frac{1}{4} \) = 25%).
\( \frac{2}{5} M = \frac{1}{4} C \).

• \( \frac{M}{C} = \frac{\frac{1}{4}}{\frac{2}{5}} = \frac{1}{4} \times \frac{5}{2} = \frac{5}{8} \)
• M : C = 5 : 8

Final Answer: 5 : 8