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For an A.P. if $\mathbf{a}_{\mathbf{2 5}}-\mathbf{a _ { 2 0 }}$ = 45, then d equals to:

A. 9 B. -9 C. 18 D. 23 Answer: Option A
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Solution(By Apex Team)

$\begin{array}{l}a_n=a+(n-1)\times d\\ \Rightarrow a_{25}=a+24d\\ \text{ and }a_{20}=a+19d\\ a_{25}-a_{20}=45\\ \Rightarrow a+24d-a-19d=45\\ \Rightarrow5d=45\\ \Rightarrow d=9\end{array}$

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