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Question: Answered & Verified by Expert
Let $a_{n}$ denote the number of all $n$-digit positive integers formed by the digits 0,1 or both such that no consecutive digits in them are 0 . Let $b_{n}=$ the number of such $n$-digit integers ending with digit 1 and $c_{n}=$ the number of such $n$-digit integers ending with digit 0 .

Question: Which of the following is correct?
MathematicsPermutation CombinationJEE Main
Options:
  • A $a_{17}=a_{16}+a_{15}$
  • B $c_{17} \neq c_{16}+c_{15}$
  • C $b_{17} \neq b_{16}+c_{16}$
  • D $a_{17}=c_{17}+b_{16}$
Solution:
2273 Upvotes Verified Answer
The correct answer is: $a_{17}=a_{16}+a_{15}$
By recurring formula, $a_{17}=a_{16}+a_{15}$ is correct

Also $c_{17} \neq c_{16}+c_{15}$

$\Rightarrow a_{15} \neq a_{14}+a_{13}\left(\because c_{n}=a_{n-2}\right)$

$\therefore$ Incorrect

Similarly, other parts are also incorrect.

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