Find the sum of the first $15$ terms of the A.P. $5, 8, 11, 14.$ ....

Open in App

Solution

Given that: a = 5, n = 15, c.d = 8 - 5 = 3
$S_{n} = \frac{n}{2} [2 a + (n - 1) d]$
$S_{15} = \frac{15}{2} [2 (5) + (15 - 1) 3] = \frac{15}{2} [10 + (14) (3)] = \frac{15}{2} \times 52$
$S_{15} = 390$

Suggest Corrections

Similar questions

24

5, 8, 11, 14, . . .

24^{t h}

15^{t h}

10 t h

5, 8, 11, 14, . . . .

15

750

15

20^{t h}

The $n^{t h}$ terms of an A.P. is given by $(- 4 n + 15)$ . Find the sum of first $20$ terms of this A.P.

Join BYJU'S Learning Program