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In a group of 30 students, how many different ways can you select a team of 8 students to participate in a quiz if exactly 4 of them must be from a specific grade?

Option: 1

29652


Option: 2

78523


Option: 3

40250


Option: 4

12650


Answers (1)

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To solve this problem, we'll consider two cases: when exactly 4 students are chosen from the specific grade and when more than 4 students are chosen from the specific grade.

Case 1: Exactly 4 students from the specific grade are chosen.

In this case, we need to select the remaining 4 students from the remaining 30-4=26 students (excluding the 4 from the specific grade).

Number of ways to select 4 students from 26=26 C4

Case 2: More than 4 students from the specific grade are chosen.

In this case, we can choose 5,6,7, or 8 students from the specific grade. Let's consider each subcase:

Sub-case 1: 5 students from the specific grade are chosen.

We need to select the remaining 3 students from the remaining 30-5=25 students.

Number of ways to select 3 students from 25=25 C3

Sub-case 2: 6 students from the specific grade are chosen.

We need to select the remaining 2 students from the remaining 30-6=24 students.

Number of ways to select 2 students from 24=24 C2

Sub-case 3:7 students from the specific grade are chosen.

We need to select the remaining 1 student from the remaining 30-7=23 students.

Number of ways to select 1 student from 23=23 C1

Sub-case 4: All 8 students from the specific grade are chosen.

There is only 1 way to select all 8 students from the specific grade.

To calculate the total number of ways to form the team, we need to sum up the possibilities from both cases and all sub-cases:

Total number of ways = Number of ways in Case 1+ Number of ways in Sub-case 1+ Number of ways in Sub-case 2 + Number of ways in Sub-case 3+ Number of ways in Sub-case 4

Total number of ways =26 C4+25 C3+24 C 2+23 C1+1

Total number of ways =14,950+25,000+276+23+1=40,250

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