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: a_{5} = - 3

Common difference = d = - 4

Now, Consider a_{5} = - 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

S_{n} = [2a + (n - 1)d]

∴ Sum of first 10 terms is given by:

S_{10} = [2(13) + (10 - 1)(-4)]

= 5[26 - 36]

= 5 × (-10)

= - 50

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