Probability Question 125

Question: Let A and B be two finite sets having m and n elements respectively such that $ m\le n. $ A mapping is selected at random from the set of all mappings from A to B. The probability that the mapping selected is an injection is

Options:

A) $ \frac{n!}{(n-m)!m^{n}} $

B) $ \frac{n!}{(n-m)!n^{m}} $

C) $ \frac{m!}{(n-m)!n^{m}} $

D) $ \frac{m!}{(n-m)!m^{n}} $

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Answer:

Correct Answer: B

Solution:

As we know the total number of mappings is $ n^{m} $ and number of injective mappings is $ \frac{n!}{(n-m)!n^{m}} $ .