Problem: Suppose Ms. Jones, an experienced painter, can paint a wall in three hours, whereas a rookie painter, Mr. King, paints the same wall in seven hours. If the two painters work together to paint the wall, how long will it take them to complete the job? Choose the most reasonable answer. Explain your decision.

1. 21 hours
2. 10 hours
3. between 5 and 10 hours
4. 5 hours
5. 4 hours
6. 3 hours
7. 2 hours
8. 1/2 hour