Q. 105.0( 3 Votes )

The 5th term of an AP is – 3 and its common difference is – 4. The sum of its first 10 terms is
A. 50

B. – 50

C. 30

D. – 30

Answer :

Let a be the first term and d be the common difference.


Given: a5 = - 3


Common difference = d = - 4


Now, Consider a5 = - 3


a + 4d = - 3


a + 4(-4) = - 3


a - 16 = - 3


a = 16 - 3


a = 13


Now, Sum of first n terms of an AP is


Sn = [2a + (n - 1)d]


Sum of first 10 terms is given by:


S10 = [2(13) + (10 - 1)(-4)]


= 5[26 - 36]


= 5 × (-10)


= - 50

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