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
(C) 25
(D) 30

AcademicMathematicsNCERTClass 10

Given: 

The common difference of an AP is $5$

To do: 

We have to find $a_{18}-a_{13}$.

Solution:

Common difference $d=5$

Let $a$ be the first term of the A.P.

$\therefore a_{18}=a+( 18-1)5$

$\Rightarrow  a_{18}=a+85$

Similarly, $a_{13}=a+( 13-1)5$

$\Rightarrow a_{13}=a+60$

$\therefore a_{18}-a_{13}=a+85-a-60=25$

Thus, $a_{18}-a_{13}=25$.

raja
Updated on 10-Oct-2022 13:27:27

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