Question

1. Find the sum upto 20 terms of the series 20 + 35 + 50 +...​

Answer 1

Answer:

Step-by-step explanation:

a = 20

d = 35 - 20 = 15

n = 20

Sum of n terms of AP, Sₙ = n/2[2a + (n-1)d]

     = 20/2[ 2*20 + (20-1)15]

      = 10[ 40 + 19*15]

      = 10[ 40 + 285]

       = 10*325

       = 3250.

Answer 2

Given:

The series - 20 + 35 + 50 +...

To Find:

The sum upto 20 terms of the series

Solution:

 Series is  20 + 35 + 50 + ...  which is  an arithmetic progression

Thus,

First term = a = 20

Common Difference = d = 35 - 20 = 15

Number of terms = n = 20

Now, using the formula -

n/2 [ 2a + ( n-1) d ]

= 20/2 [ 2 x 20 + ( 20 - 1) 15 ]

= 10 [ 40 + 285 ]

= 10 x 325

= 3250

Answer: The sum upto 20 terms of the series is 3250.