Question

Q-16 The sum of the fourth and twelfth term of an arithmetic
progression is 20. What is the sum of the first 15 terms of the
arithmetic progression?
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Answer 1

Answer:

Given that :

$\sf{a_{4} + a_{12} = 20}$

By using :

$\sf{a_{n} = a + (n - 1)d}$

=》 a + 3d + a + 11d = 20

=》 2a + 14d = 20 ...(1)

We need to find :

$\sf{s_{15}}$

By using :

$\sf{s_{n} = \frac{n}{2} (2a + (n -1 )d)}$

=》 $\sf{s_{15} = \frac{15}{2}(2a + 14d)}$

Put ...(1) , you get :

Sum of 15 terms is = 150

Answer 2

Note : Check This Attachment ⬆

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