In an examination of 9 papers a candidate has to pass in more papers t...
The candidate is unsuccessful if he fails in 9 or 8 or 7 or 6 or 5 papers.
∴ the number of ways to be unsuccessful
In an examination of 9 papers a candidate has to pass in more papers t...
Problem Analysis:
The candidate needs to pass more papers than the number of papers in which he fails in order to be successful. Let's assume that the candidate passes x papers and fails y papers. According to the given condition, x > y.
Solution:
To find the number of ways in which the candidate can be unsuccessful, we need to consider all possible values of y and calculate the corresponding values of x.
Case 1: y = 0
If the candidate fails in 0 papers, it means he passes in all 9 papers. However, according to the given condition, he needs to pass more papers than the number of papers in which he fails. Therefore, this case is not valid.
Case 2: y = 1
If the candidate fails in 1 paper, he can pass in any number of papers from 2 to 9. The number of ways in which he can pass in 2 papers is 1, the number of ways in which he can pass in 3 papers is 8C3 = 56, and so on. The total number of ways in which he can be unsuccessful in this case is the sum of these values, which is given by:
1 + 8C3 + 8C4 + 8C5 + 8C6 + 8C7 + 8C8 + 8C9 = 1 + 56 + 70 + 56 + 28 + 8 + 1 = 220
Case 3: y = 2
If the candidate fails in 2 papers, he can pass in any number of papers from 3 to 9. Similarly, we can calculate the number of ways in which he can be unsuccessful in this case:
1 + 7C3 + 7C4 + 7C5 + 7C6 + 7C7 + 7C8 + 7C9 = 1 + 35 + 35 + 21 + 7 + 1 = 100
Case 4: y = 3
Similarly, if the candidate fails in 3 papers, he can pass in any number of papers from 4 to 9. We can calculate the number of ways in which he can be unsuccessful in this case:
1 + 6C3 + 6C4 + 6C5 + 6C6 + 6C7 + 6C8 + 6C9 = 1 + 20 + 15 + 6 + 1 = 43
Case 5: y = 4
1 + 5C3 + 5C4 + 5C5 + 5C6 + 5C7 + 5C8 + 5C9 = 1 + 10 + 5 + 1 = 17
Case 6: y = 5
1 + 4C3 + 4C4 + 4C5 + 4C6 + 4C7 + 4C8 + 4C9 = 1 + 4 + 1 = 6
Case 7: y = 6
1 + 3C3 + 3C4 + 3