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In a group of 26 students, how many different ways can you select a team of 7 students to participate in a quiz if at least 4 of them must be from a specific grade?

Option: 1

9632


Option: 2

8462


Option: 3

1771


Option: 4

1025


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 5 or more 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 3 students from the remaining 26-4=22 students (excluding the 4 from the specific grade).

Number of ways to select 3 students from 22=22 C 3

Case 2: 5 or more students from the specific grade are chosen.

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

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

We need to select the remaining 2 students from the remaining 26 - 5=21 students.

Number of ways to select 2 students from 21=21 C 2

Sub-case 2: 6 students from the specific grade are chosen.
We need to select the remaining 1 student from the remaining 26-6=20 students.

Number of ways to select 1 student from 20=20 C1

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

There is only 1 way to select all 7 students from the specific grade.

To calculate the total number of ways to form the tearn, 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

Total number of ways =22 C3+21 C2+20 C1+1

Now, let's calculate the value:

Total number of ways =1540+210+20+1=1771

Therefore, there are 1771 different ways to select a team of 7 students to participate in the quiz, where at least 4 of them must be from a specific grade.

Posted by

Divya Prakash Singh

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