Question

Two $A.P.$s have the same common difference. The first term of one of these is $1$ and that of the other is $8$. Then the difference between their $4^{th}$ terms is

• A. $-1$
• B. $-8$
• C. $7$
• D. $-9$

Answer 1

Answer: (C)

$7$

Let the common difference for the two AP's be $d$.
Given,
First term of first AP is $1$,
First term of second AP is $8$.
Then,
Fourth term of first AP$=1+3d$
Fourth term of second AP$=8+3d$
Given the difference between the two terms as $7$.
Then,
$(8+3d)-(1+3d)=7$