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If n(A)=15 and n(B)=10, then number of i...

If `n(A)=15` and `n(B)=10`, then number of injective (one-one) mapping from A into B is

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We know that in onto mapping, each image must be assigned atleast one pre-image.
This is equivalent to number of ways in which 5 different balls (pre-images) can be distributed in 3 different boxes (images), if no box remains empty. The toal number of onto mappings from A to B.
`=3^(5)-.^(3)C_(1)(3-1)^(5)+.^(3)C_(2)(3-2)^(5)`
`=243-96+350`
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