Question

The ${21}^{st}$ term of the AP whose first term is $3$ and second term is $4$, is

• A. $17$
• B. $19$
• C. $21$
• D. $23$

Answer 1

The correct option is D $23$

Given,
$a_1=3$, $a_2=4$.
$\therefore$ Common difference, $d=1$.
Using the formula for $n^{th}$ term of an $A.P.$
$a_n=a+(n-1)d$

For, $n=21$,
$a_{21}=3+(21-1)\times 1$
$a_{21}=3+20\times 1$
$a_{21}=23$