Find the sum of the first twenty odd positive integers that have a remainder of 1 when divided by 3
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: .Sn .= .½n[2a + (n-1)d]
Therefore: .S20 .= .½(20)[2·7 + 19·6] .= .1280