Maths Olympiad Prep

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Combinatorics Difficulty 3.7 AMC 10/12 Find the answer

In a senior high school's mathematics class, there are six subjects to be scheduled on Wednesday, with four periods in the morning and three in the afternoon. Both the Chinese language and mathematics must be scheduled for two consecutive periods, while English, physics, chemistry, and biology can each be scheduled for at most one period. There are \_\_\_\_\_\_ different possible arrangements for the schedule.

A number or a short expression. Spacing and $ signs are ignored.

Solution

According to the problem statement, we discuss two scenarios:

1. Both Chinese and mathematics are scheduled in the morning. For the arrangement of Chinese and mathematics, there are 2 ways (either can be first). For the remaining 4 subjects, we need to choose 3 to be scheduled in the afternoon. This can be done in A43A_4^3 ways. Thus, there are 2×A43=2×4×3×2=482 \times A_4^3 = 2 \times 4 \times 3 \times 2 = 48 arrangements for this scenario.

2. Chinese and mathematics are scheduled one in the morning and the other in the afternoon.
- If Chinese is in the morning, there are 3 ways to arrange it (as one slot is taken by mathematics). For mathematics in the afternoon, there are 2 ways. We need to choose 3 from the remaining 4 subjects to arrange at other times, which gives us A43A_4^3 possibilities. Therefore, there are 3×2×A43=3×2×4×3×2=1443 \times 2 \times A_4^3 = 3 \times 2 \times 4 \times 3 \times 2 = 144 ways for this arrangement.
- By symmetry, if mathematics is in the morning and Chinese is in the afternoon, there are also 144 ways.

By combining the scenarios, the total number of different possible arrangements is 48+144+144=33648 + 144 + 144 = 336. Hence, the solution is:

336 \boxed{336}

The principle of addition is applied here to combine the scenarios, and the arrangement is computed by considering the given constraints and focusing on elements with restrictions first.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.