In an examination a candidate has to pass in each of the 5 subjects. In how many ways he can fail ?

  1. 31
  2. 20
  3. 25
  4. 30

Answer (Detailed Solution Below)

Option 1 : 31
Free
NDA 01/2025: English Subject Test
30 Qs. 120 Marks 30 Mins

Detailed Solution

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Concept:

The number of ways to select r things out of n given things wherein r ≤ n is given by:

Calculation:

Given: There are 5 subjects and for a student to pass in an examination the students has to pass in each of the 5 subjects.

Here, we have to find in how many ways a student can fail in the examination.

In order to fail in the examination the student can fail in 1 or 2 or 3 or 4 or 5 subjects out of the 5 subjects in each case.

Case 1: Student fails in any 1 subject out of the 5 subjects.

No. of ways in which student can fail in any 1 subject out of the 5 subjects = 

Case 2: Student fails in any 2 subjects out of the 5 subjects.

No. of ways in which student can fail in any 2 subjects out of the 5 subjects = 

Case 3: Student fails in any 3 subjects out of the 5 subjects.

No. of ways in which student can fail in any 3 subjects out of the 5 subjects = 

Case 4: Student fails in any 4 subjects out of the 5 subjects.

No. of ways in which student can fail in any 4 subjects out of the 5 subjects = 

Case 5: Student fails in all 5 subjects.

No. of ways in which student can fail all 5 subjects. = 

∴ Total number of ways in which a student can fail in an examination =  +  +  +  +  = 31

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