Bunuel
How many different 5-letter groups can be selected from the letters of the word "CANADIANS"?
A. 21
B. 36
C. 37
D. 41
E. 42
C AAA NN D I S
Case 1: The selected letter group doesn't have any repeating alphabets
- Number of ways of selecting 5 alphabets out of 6 alphabtes = \(^6C_5\)
Total number of ways = 6
Case 2: The selected letter group has exactly two repeating alphabets
- The two repeating alphabets can be either 'A' or 'N'. The number of ways of selecting A or N = \(^2C_1\)
- The remaining three alphabets can be selected in \(^5C_3 \) ways
Total number of ways = 2 * 10 = 20
Case 3: The selected letter group has exactly three repeating alphabets
- The repeating alphabet can only be A. The number of ways of selecting A = \(1\)
- The remaining two alphabets can be selected in \(^5C_2 \) ways
Total number of ways = 10 * 1 = 10
Case 4: The selected letter group has two pairs of repeating alphabets and one non-repeating alphabet
- The two repeating alphabets can only be A and N. We need to select both. The number of ways of selecting A and N= \(1\)
- The remaining alphabet can be selected in \(^4C_1 \) ways
Total number of ways = 4 * 1 = 4
Case 5: The selected letter group has only repeating alphabets
- The repeating alphabets can only be A and N. We need to select both. The number of ways of selecting A and N= \(1\)
Total number of ways =1
Total:
Sum of each cases = 6 + 20 + 10 + 14 + 1 = 41
IMO Option D