Question

what is the sum of the first 20 terms of an A.P , if the a = 4 and t20 = 36?
a. 40
b.200
c.400
d.800​

Answer 1

Answer:

t20= 36

4+(20-1)d = 36

19d =32

d=32/19

s20 = 20/2 (8+19×32/19)

= 10(8+32)

= 10×40

=400

Answer 2

Answer:

400

Step-by-step explanation:

t20=36

4+(20-1)d=36

4+(19)d=36

(19)d=36-4

19d=32

s20=20/2(8+19×32/19)

=10(8+32)

=10(40)

=400

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