i have also same idea as you solve this question but i tried a different approch that does not work , image of my solution is given above plese tell me my mistake , your answer is right

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Sachin85
asked
in Combinatory
May 15, 2022

141 views
2 votes

Best answer

With 26 alphabet for a 5 letter word we can have $26^{5}$ possible words as each 5 position can have 26 possible alphabet.

we need no of word which contains at least one ‘A’.

This is same as

Total number of words – Number of words with no ‘A’

Now,

Number of words with no ‘A’ =$25^{5}$ as, each 5 position can have 25 possible alphabet as we exclude ‘A’.

so ,

Total number of words which contains at least one ‘A’ =$26^{5}-25^{5}$.

we need no of word which contains at least one ‘A’.

This is same as

Total number of words – Number of words with no ‘A’

Now,

Number of words with no ‘A’ =$25^{5}$ as, each 5 position can have 25 possible alphabet as we exclude ‘A’.

so ,

Total number of words which contains at least one ‘A’ =$26^{5}-25^{5}$.

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