865Is (c) the correct answer?
If A = {1,2,3,4....18,19} then the number of functions f : A→A such that f(x)=y and sum of digits of x is equal to the sum of digits of y is
(a) 540 (b) 219 (c) 218 (d) 720
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4 Answers
865The ordered pairs (x, y) satisfying the given condition are (1, 1), (2, 2),...,(19, 19); (1, 10), (2, 11), (3, 12),...,(9, 18); (10, 1), (11, 2),...,(18, 9). As the domain is A, we must assign values to each x=1, 2,..., 19. Now, for x=1, we have two choices for y(1 and 10), similarly for x=2, 3,...,18 whereas for x=19 we have only one possible value of y. Therefore the answer will be 218.
Soumak Roy thank you buddy ..Upvote·0· Reply ·2014-04-14 09:04:21