Five men started a job expected to be done in 15 days. After 5 days, 10 women joined them and together they finished in the next 5 days. If 10 women alone had started the job, in how many days would they have completed it?

Introduction / Context:
Infer women-to-man efficiency from the mixed phase, then apply it to compute the time for 10 women to complete the full job alone.

Given Data / Assumptions:

• 5 men for 15 days → job size = 75 man-days.
• After 5 days (25 man-days done), 10 women join and the remaining is done in 5 more days.

Concept / Approach:
Use remaining work and team rate over the next 5 days to deduce 1 woman in man-equivalents, then compute the women-only time.

Step-by-Step Solution:

Verification / Alternative check:
Back-substitution to mixed phase confirms consistency with the observed completion time.

Why Other Options Are Wrong:
They reflect incorrect conversion between women and men or wrong total job size.

Common Pitfalls:
Confusing “man-days” with “men-days” arithmetic; always treat efficiency conversion consistently.

Final Answer:
15 days