Question

calculate the sum of first 20term's of the sequence 3,7,11

Answer 1

Step-by-step explanation:

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Answer 2

Step-by-step explanation:

First find the 20 th term:

a20=a1+(n−1)d        =3+19*(4)=79

Then find the sum:

Sn=n(a1 + an)/2=20*(3+79)*1/2=20*(41)=820