Question

find the sum of first 20 terms of the arithmetic progression 3, 8, 13​

Answer 1

Step-by-step explanation:

common difference (d)=5

first term(t n)=3

n=20

$tn = a + (n - 1)d$

$t20 = 3 + (20 - 1)5 = 3 + 19 \times 5$

$t20 = 98$

Answer 2

☆ ΛПƧЩΣЯ ☆

$given \\ a = 3 \: \: d = 5 \: \:n = 20 \\ s20 = \frac{n}{2} (2a + (n - 1)d) \\ = \frac{20}{2} (2(3) + (20 - 1)5) \\ = 10(6 + 19 \times 5)$

$= 10 \times 101 \\ = 1010$

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