Explanation:

- Given: 10 men or 12 women can complete the work in 10 days.

- Work Equivalent: 1 man's 1-day work = Work/100, 1 woman's 1-day work = Work/120 (since 10 men can do the same work as 12 women in 10 days).

- 5 men and 2 women working together have a combined work per day: $\frac{5}{100}+\frac{2}{120}$.

- Simplifying: $\frac{5}{100}+\frac{1}{60}=\frac{1}{20}$.

- Days required: Reciprocal of daily work = 20 days.

- Correct answer: Option 3 - 20 days.

Answer: Option 3 - 20