Question

. Find the sum of the first 400 terms of an A. P. whose first term is 40 and the 400th term is 120

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Answer 1

Step-by-step explanation:

given:

n=400

a=40

l=120

solution:

Sn =

Answer 2

Answer:

sum = 32,000

Step-by-step explanation:

Here , a = 400 ,

tn = 120

n = 400

Now , Sn = n ÷ 2 × ( a + tn )

= 400 ÷2 × ( 40 + 120 )

= 200 × 160

= 32,000

Therefore , sum of first 400 terms of the A.P is

32,000