Pete can paint a room in $10$ hours alone, and Alicia can paint the same room in $8$ hours alone. Working together at a constant pace (without interfering with each other), how long will it take them to paint the room?

Hourly rates: - Pete: $\tfrac{1}{10}$ of the room per hour. - Alicia: $\tfrac{1}{8}$ of the room per hour. Combined rate: $\tfrac{1}{10} + \tfrac{1}{8} = \tfrac{4}{40} + \tfrac{5}{40} = \tfrac{9}{40}$ of the room per hour. Time for one full room: $t = \dfrac{1}{9/40} = \dfrac{40}{9}$ hours $\approx 4.444$ hours. Convert to hours and minutes: $\tfrac{4}{9} \times 60 = \tfrac{240}{9} \approx 26.67 \approx 27$ minutes. So about $4$ hours $27$ minutes. - Trap B ($5$) is an arithmetic-mean style guess that ignores the rate model. - Trap C ($9 = 10 - 1$) is unrelated. - Trap D ($18 = 10 + 8$) adds solo times — wrong direction. The answer must be **less than the faster solo time** ($8$ hours). $40/9 \approx 4.44$ is also more than half of $8$ — both bounds are respected.