2007-09-19 13:42:26 · 12 answers · asked by Gavin J 2 in Science & Mathematics ➔ Mathematics
Sum is 171.
A fast way to find the sum is:
Consider 18 + 1 = 19, then 2 + 17 = 19, 3 + 16 = 19, etc. You will get 9 pairs of terms that add up to 19. 19 * 9 = 171.
2007-09-19 13:46:37 · answer #1 · answered by SoulDawg 4 UGA 6 · 0⤊ 2⤋
if you take 19 X 9 = 171
19 if 18 + 1 , 17 + 2 , 16 + 3 and so on and 9 if half of 18
2007-09-19 13:54:10 · answer #2 · answered by heat_3636 2 · 0⤊ 0⤋
To find the sum of consecutive integers, 1 to m,
= (1 + m)(m/2)
= (1 + 18)(18/2) = 19 * 9 = 171
2007-09-19 13:49:13 · answer #3 · answered by Marvin 4 · 0⤊ 0⤋
S=1+2+3+4......+18
S=18+17+16.....+1
2S= 19+19+19...+19
2S= 19 *18
2S=342
S= 171
2007-09-19 13:52:20 · answer #4 · answered by . 2 · 0⤊ 0⤋
1+2+3+4+...+n = n(n+1)/2
1+2+3+4+....+18
= 18*19/2
= 19*9
= 171
2007-09-19 13:47:21 · answer #5 · answered by gudspeling 7 · 0⤊ 0⤋
the total of 1...n=(n*(n+1))/2
case in point=342/2=171
want to check just add 1+2+3+4+5+6+7+8=36
+80+36+9+10=171
why +80 and 36 again
because
1+2=3
11+12=23
and
1+2+3+4=10
11+12+13+14=50
2007-09-19 14:01:00 · answer #6 · answered by GOLD-FLAW 2 · 0⤊ 0⤋
make pairs
1 and 18
2 and 17
3 and 16
4 and 15
5 and 14
6 and 13
7 and 12
8 and 11
9 and 10
that is 9 pairs of 19
so 9 x 19 = 171
2007-09-19 13:48:36 · answer #7 · answered by sfroggy5 6 · 0⤊ 0⤋
1+2=3+3=6+4=10+18=28
Pretty easy - just do one at a time. Kind of self explanatory.
2007-09-19 13:48:16 · answer #8 · answered by Anonymous · 0⤊ 1⤋
making pairs is not bad if you are only summing a small amount of integers.. otherwise, use the general form: n(n+1)/2 so its (18*19)/2
btw, i think gauss figured that pairs thing up at like eight yrs old.
2007-09-19 13:51:27 · answer #9 · answered by Olds442 2 · 0⤊ 0⤋
its 171
2007-09-19 13:50:23 · answer #10 · answered by swissmiss1002 2 · 0⤊ 0⤋