answer
2007-10-29 20:14:49 · 12 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
10 * 11 / 2 = 55
In general for the sum of 1 through n:
n (n + 1) / 2
So, now you tell me what is 1+2+3+ ... +98+99+100? No calculator allowed.
2007-10-29 20:19:13 · answer #1 · answered by Puzzling 7 · 2⤊ 0⤋
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = 55
2007-11-01 16:05:46 · answer #2 · answered by Rayan Ghazi Ahmed 4 · 0⤊ 0⤋
1+2+3+4+5+6+7+8+9+10
number of terms (n)= 10
sum = n(n+1)/2 = 10(10+1)/2 = 110/2 = 55
2007-10-29 21:02:41 · answer #3 · answered by Anonymous · 0⤊ 0⤋
a=1+2+3+4+5+6+7+8+9+10
a=10+9+8+7+6+5+4+3+2+1
2a=11+11+11+11+11+11+11+11+11+11
2a=10(11)
a= 5(11)
a=55
clear about this, this method is used by famous mathematician karl gauss, when his teacher ask him to count all numbers from 1 until 100, he solved in a short time, and at that time, he was only a child.
2007-10-30 01:10:18 · answer #4 · answered by datuk M 2 · 0⤊ 0⤋
1+2+3+4+5+6+7+8+9+10=55
another solution
there are ten numbers
the first number is 1
and the last number is 10
sum=n(a1+a10)/2=10(1+10)/2=5(11)=55
2007-10-29 20:23:27 · answer #5 · answered by ptolemy862000 4 · 1⤊ 0⤋
1+10=11
2+9=11
3+8=11
4+7=11
5+6=11
therefore if you sum the last and the first no. and then multiply the answer by n/2 (in this question:10/2=5) you'll find the answer.;)
1+10=11
10/2=5
11*5=55
good luck
2007-10-29 21:06:03 · answer #6 · answered by Anonymous · 0⤊ 0⤋
55
2007-10-29 21:01:02 · answer #7 · answered by terrorblade 3 · 0⤊ 0⤋
55
2007-10-29 20:18:40 · answer #8 · answered by Aimee 3 · 1⤊ 2⤋
55
2007-10-29 20:18:36 · answer #9 · answered by Anonymous · 1⤊ 2⤋
55 use a calculator next time
2007-10-29 20:19:10 · answer #10 · answered by Anonymous · 0⤊ 3⤋