Question

Calculate the sum of first 30 terms of the A.P.$-2,-5,-8,-\mathrm{11....}$

• A. $-1165$
• B. $-1265$
• C. $-1365$
• D. $-1465$

Answer 1

Answer: (C)

$-1365$

First term of the given arithmetic series = -2
Second term of the given arithmetic series = -5
Third term of the given arithmetic series = -8
Fourth term of the given arithmetic series = -11
Now, Second term - First term = -5 - (-2) = -3
Third term - Second term = -8 - (-5) = -3
Therefore, common difference of the given arithmetic series is -3.
The number of terms of the given A. P. series (n) = 30
We know that the sum of first n terms of the Arithmetic Progress, whose first term = a and common difference = d is
Sn=(n/2)[2a+(n−1)d]Sn=n2[2a+(n−1)d]