Question

If $p^{th}$ term of a list of numbers $21,42,63,....$ is $420$ then ${}^{\prime }{p}^{\prime }$ is____

• A. $20$
• B. $21$
• C. $23$
• D. $19$

Answer 1

Answer: (A)

$20$

First term$=21$

Common Difference$=2ndterm-1stterm=42-21=21$

$\therefore p^{th}term=a+(n-1)d$

$=21+(p-1)21$

$=21p+21-21=21p$

$\therefore 21p=420$

$\therefore p=20$