If the common difference of an A.P. is 3, then a_ 20 - a_ 15 is : - Vidyadip

MCQ

If the common difference of an $A.P$. is $3,$ then $a_{20}- a_{15}$ is :

A
$5$
B
$3$
✓
$15$
D
$20$

✓

Answer

Correct option: C.

$15$

Let the first term of the $A.P$. be $a$.
$ a_n=a(n-1) d $
$ a_{20}-a_{15}=[a+(20-1) d]-[a+(15-1) d] $
$= 19d - 14d$
$= 5d$
$= 5 \times 3$
$= 15$

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