MCQ
Choose the correct answer from the given four options : If the common difference of an $AP$ is $5,$ then what is $a_{18}– a_{13}?$
- A$5$
- B$20$
- ✓$25$
- D$30$
✓
Answer
Correct option: C.
$25$
Given, the common difference of $AP$
i.e.$,d = 5$
$ {\left[\therefore a_n=a+(n-1) d\right]} $
Now $,a_{18}-a_{13}=a+(18-1) d-[a+(13-1) d] $
$ a_{18}-a_{13}=a+17 \times 5-a 12 \times 5 $
$ a_{18}-a_{13}=85-60 $
$ a_{18}-a_{13}=25 $
i.e.$,d = 5$
$ {\left[\therefore a_n=a+(n-1) d\right]} $
Now $,a_{18}-a_{13}=a+(18-1) d-[a+(13-1) d] $
$ a_{18}-a_{13}=a+17 \times 5-a 12 \times 5 $
$ a_{18}-a_{13}=85-60 $
$ a_{18}-a_{13}=25 $
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