# Thread: Sum of integers

1. ## Sum of integers

Find the sum of the first twenty odd positive integers that have a remainder of 1 when divided by 3

2. well you have...

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

are your first 20 odd positive integers.

the numbers that will give you a remember of 1 when divided by 3 is

1 + 7 + 13 + 19 + 25 + 31 + 37 = 133

3. Originally Posted by smoothi963
well you have...

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

are your first 20 odd positive integers.

the numbers that will give you a remember of 1 when divided by 3 is

1 + 7 + 13 + 19 + 25 + 31 + 37 = 133
u got the whole idea wrong

4. Hello, Rimas!

Find the sum of the first twenty odd positive integers
that have a remainder of 1 when divided by 3

The numbers are: .7, 13, 19, 25, . . .

This is an arithmetic sequence with first term a = 7 and common difference d = 6.

The sum of an A.S. is: .S
n .= .½n[2a + (n-1)d]

Therefore: .S
20 .= .½(20)[2·7 + 19·6] .= .1280