Question

How many terms of the A.P. 3, 9, 15, 21, ... must be taken to give a sum of 1875​

Answer 1

Step-by-step explanation:

For sum of ( Sn ) = 1875 -

here a = first term = 3 , d = common difference = 6

Using Formula -

Sn = n / 2 × [ 2a + ( n - 1 ) × d ]

1875 × 2 = n × [ 6 + 6n - 6 ]

3750 = n × 6n

n^2 = 3750 / 6

n = √ 625

n = no. of terms = 25

hope this helps...