Question

The sum of first 20 and 50 terms of an ap is 400 and 2500

Answer 1

Answer:

1   , 3  , 5   , 7   ......................

Step-by-step explanation:

Let say first term = a

common difference = d

Sum of n terms = (n/2)(a + a + (n-1)d)

= (n/2)(2a + (n-1)d)

Sum of 20 terms = 400

=> (20/2)(2a + 19d) = 400

=> 2a + 19d = 40

Sum of 50 terms = 2500

=> (50/2)(2a + 49d) = 2500

=> 2a + 49d = 100

49d - 19d = 100 - 40

=> 30d = 60

=> d = 2

=> 2a + 19*2 = 40

=> 2a = 2

=> a = 1

AP

1   , 3  , 5   , 7   ......................