Question

find the sum of first 20terms of an ap3,7,11,15​

Answer 1

Answer:

a=3

d=4

n=20

Step-by-step explanation:

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

=20/2 (2×3+(20-1)4)

=10 (82)

=820

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Answer 2

Answer:

the sum is 820

Step-by-step explanation:

Here,

a = 3, d = 4, n = 20

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

S = 20/2[2.3 + (20-1) 4]

S = 10[6+19.4]

S = 10 [6+ 76]

S = 10.82

S = 820