If the common difference of an

Question:

If the common difference of an $\mathrm{AP}$ is 5 , then what is $\mathrm{a}_{18}-\mathrm{a}_{13}$ ?

(a) 5

(b) 20

(c) 25

(d) 30

Solution:

(c) Given, the common difference of AP i.e., d = 5

Now, $\quad a_{18}-a_{13}=a+(18-1) d-[a+(13-1) d] \quad\left[\because a_{n}=a+(n-1) d\right]$

$=a+17 \times 5-a-12 \times 5$

$=85-60=25$

 

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