Let A=\1, 2, 3, 4, 5, 6\. The number of one-one functions f : A A such that f(1) 3, f(3) 4 and f(2)+f(3)=5, is .
Answer
72
Solution
f(2)+f(3)=5 with distinct values in A: (f(2), f(3))=(1, 4), (4, 1), (2, 3), (3, 2) (all satisfy f(3) 4)
Case (1, 4) or (4, 1): f(1) 3, not 1 or 4 f(1) \3, 5, 6\: 3 ways each
Case (2, 3) or (3, 2): f(1) 3, not 2 or 3 f(1) \4, 5, 6\: 3 ways each
Remaining elements 4, 5, 6 map one-one onto the 3 remaining images: 3!=6 ways
Total =4 3 6=72
Answer: 72