Question

TWO APs have the same common difference. The first term of these is -1 and that of the other
is-8. The difference between their 4th terms
7
-1
-8
- 9​

Answer 1

$Let \: the \: common \: difference \: be \: d.$

$first \: term \: of \: AP1 = -1$

$4th \: term = -1 + (4-1) d = -1 + 3d$

$first \: term \: of \: AP2 = -8$

$4th \: term \: = -8 + (4-1) d = -8 + 3d$

$Difference = -1 + 3d - (-8 +3d) = -1 + 3d + 8 - 3d </p><p> = 7.$

Hence, the correct answer is 7.