JEE Main & Advanced Sample Paper JEE Main Sample Paper-5

  • question_answer
    10 different letters of english alphabet are given words of 5 letters are formed from these given letters. How many words are formed when at least one letter is repeated?

    A)  69760                  

    B)  2912                

    C)  98748                  

    D)  987147

    Correct Answer: A

    Solution :

     Idea Here, number of permutation of n dissimilar things taken r at a time \[{{=}^{n}}{{p}_{r}}=\frac{n!}{(n-r)!}\]repetition is not allowed total ways \[={{n}^{r}}\]Number of 5 letters word if at least one letter is repeated is equal to = Total possible 5 letters word Number of 5 letters word when repetition is not allowed \[={{10}^{5}}-10\times 9\times 8\times 7\times 6\] \[={{10}^{5}}-30240\] \[=69760\] TEST Edge Fundamental theorem of permutation and their application based questions are asked. To solve such type of question, students are advised to understand the concept of fundamental theorem.

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