Question

find the sum of 1st 20 term of the series 4+7+10+....

Answer 1

Step-by-step explanation:

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

=>>S20 = 20/2[2×4 + (19)3]

=10(8 + 57)

= 650

Answer 2

The sum of first 20 terms is "650".

Step-by-step explanation:

$The \ given \ series \ is:\\4+7+10+...\\Where,\\The \ first \ term,a,a_{1}=4\\ The \ second \ term,a_{2}=7\\Difference,d=a_{2}-a_{1}=7-4=3\\n=20\\As \ we \ know,\\S_{20}=\frac{n}{2}[2a+(n-1)d]\\S_{20}=\frac{20}{2}[2(4)+(20-1)3]\\S_{20}=10[8+19(3)]\\S_{20}=10[8+57]\\S_{20}=10\times 65\\S_{20}=650$

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