Question

13. The sum of the first 20 terms of the A.P.5, 8,
11. 14.........is​

Answer 1

Answer:

5700

Step-by-step explanation:

a1=5

d=3

n=20

S20=n/2 (2a+(n-1)d)

= 20/2(2×5+(20-1)3) = 10(10+19×3) = 10(570) =5700

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Answer 2

Answer:

Sum of 20terms is 670

Step-by-step explanation:

Here,a=5 ;d=8-5=3; n=20

We know that

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

S =20/2[2(5)+(20-1)3]

= 10[10+(19×3)]

=10[10+57]

=10×67

=670

Hope this helps you....