SOLUTION: Use Gauss'e approach to find the following sum (Do not use formulas): 3+9+15+21+...69 The sum of the sequence is _____?

Algebra.Com
Question 894167: Use Gauss'e approach to find the following sum (Do not use formulas):
3+9+15+21+...69
The sum of the sequence is _____?
Answer by Edwin McCravy(20056)   (Show Source): You can put this solution on YOUR website!
We have these 12 terms to add:

3+9+15+21+27+33+39+45+51+57+63+69

The 1st and 12th terms have sum  3+69 = 72
The 2nd and 11th terms have sum  9+63 = 72
The 3rd and 10th terms have sum 15+57 = 72
The 4th and  9th terms have sum 21+51 = 72
The 5th and  8th terms have sum 27+45 = 72
The 6th and  7th terms have sum 33+39 = 72

That's 6 times 72 or 432.

Edwin
RELATED QUESTIONS

Use Gauss approach to find the sum. (do not use formulas) 1+3+5+7+...+997 (answered by richwmiller)
Use Gauss's approach to find the following sums(do not use formulas). a.... (answered by MathLover1)
use Gauss approach to find the following signs (do not use formulas0. a.... (answered by rothauserc)
Use gauss approach to find the sum of... (answered by Edwin McCravy)
Write the formula for the general (nth term) of the following arithmetic sequence. (Do... (answered by fractalier)
Use the gauss approach to find a formula for the sum of the even numbers from 2 to 2n... (answered by ikleyn)
Use the gauss approach to find a formula for the sum of the even numbers from 2 to 2n... (answered by solver91311)
Use the approach in Gauss's Problem to find the following sums of arithmetic sequences... (answered by Edwin McCravy)
Can someone please help me? 1. Find the sum of each arithmetic series. Part I: -15 + -3 (answered by josgarithmetic)