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5 votes
12+17+22+...+102

i will give brailiest to who answers first and is right

2 Answers

6 votes


a = 7


d = 12 - 7 = 5


L = 102


\implies a + (n-1)d = 102


\implies 7 + (n-1)(5) = 102


\implies (n-1)(5) = 95


\implies n - 1 = 19


\implies n = 20


\text{Required sum = n/2} \ (a + L)


= 20 /2 \ ( 7 + 102)


= 10 * 109


\bold{= 1090}

User Perennialista
by
8.3k points
2 votes

Answer:

The sum is 1090

Explanation:

S=7+12+17+22+...+102 ---> reason=5

We define the values, before starting:

Ratio = r , Term n = Tn , Term number = n , Term one = T1

To do this we first find the term number of 102, with the following formula:

Tn = t1 + (n - 1) r

102 = 7 + (n - 1) 5

102 = 7 + 5n - 5

102 = 5n + 2

100 = 5n

20 = n

Then we realize that 102 is the term N°20, now what we have to do is find the sum of the arithmetic series, with the following values and the following formula:

t1 = 7 , tn = 102 , n = 20

S = (
(t1+tn)/(2)) . n

S = (
(7+102)/(2)) . 20

S = 109 . 10

S = 1090

User Abs
by
8.5k points

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