Teams A, B, and C consist of five, eight, and ten members, respectively, such that every member within a team is equally productive. Working separately, teams A, B, and C can complete a certain job in 40 hours, 50 hours, and 4 hours, respectively. Two members from team A, three members from team B, and one member from team C together start the job, and the member from team C leaves after 23 hours. The number of additional member(s) from team B, that would be required to replace the member from team C, to finish the job in the next one hour, is
Answer: A
Key idea: Work out the rate of one member of each team, measured in "jobs per hour".
1. One A member: \( \frac{1}{40 \times 5} = \frac{1}{200} = \frac{2}{400} \). One B member: \( \frac{1}{50 \times 8} = \frac{1}{400} \). One C member: \( \frac{1}{4 \times 10} = \frac{1}{40} = \frac{10}{400} \).
2. Starting group rate: \( 2 \times \frac{2}{400} + 3 \times \frac{1}{400} + \frac{10}{400} = \frac{17}{400} \) per hour.
3. In 23 hours: \( \frac{391}{400} \) done, leaving \( \frac{9}{400} \) to finish in 1 hour.
4. Without the C member the group does \( \frac{7}{400} \) per hour, short by \( \frac{2}{400} \), which is the work of 2 B members.
Tip: Taking total work = 400 units makes every rate a whole number: A = 2, B = 1, C = 10 units per member per hour.
Hence, the answer is (A) 2.