# Ok, I give up - middle school math. . .

#### episodic

##### Lifer
Find a novel way to add all of the integers between 1 and 100

Method must not include a calculator - nor may it include 1+2+3 - figuring it out the old fashioned way.

It must be understood and explainable by a 6th grader. . .

sigh. . .

#### Shawn

##### Lifer
I used to know how to do this, but I have long since forgotten.

#### George P Burdell

##### Lifer
n (n + 1) /2 (if i remember correctly)

edit: where n = 100

#### fallenangel99

##### Golden Member
k(2n+k-1) / 2
k = count of integers
n = starting number

(the formula is for consecutive integers)
k = 100-1 = 99+1 = 100 integers
n =1

I know this formula because I am taking my GMAT exam tomm.

#### Gibson486

##### Lifer
they learn about series in the 6th grade now??? is this in China?

1 + 100 = 101
2 + 99 = 101
3 + 98 = 101
4 + 97 = 101

#### Alone

##### Diamond Member
Fvck that I still don't know this ******.

#### Savij

##### Diamond Member
1+99 = 100
2+98=100
.
.
.
49+51=100
+50
+100

is the same as 49*100+150

#### episodic

##### Lifer
Thanks - found another one too googling around - add 1st and last number 1+100 = 101 - ask yourself how many 'pairs' are between the 2 numbers (100/2) - there are 50 pairs - multiply that times 101 = 5050. . .

The other ways are cool too

Not china - rural south. . ., hard teacher.

#### thesurge

##### Golden Member
By induction,

n=1
(1)(1+1)/2=1=1

n=n+1
n(n+1)/2+n+1=(n+1)((n+1)+1)/2

See:
1+100=101
2+99=101
...
50 pairs of 101=...

look up gauss...

#### ungsunghero

##### Golden Member
Originally posted by: episodic
Thanks - found another one too googling around - add 1st and last number 1+100 = 101 - ask yourself how many 'pairs' are between the 2 numbers (100/2) - there are 50 pairs - multiply that times 101 = 5050. . .

The other ways are cool too

Not china - rural south. . ., hard teacher.

That's how I learned it back in elementary school.

#### Gibson486

##### Lifer
Originally posted by: episodic
Thanks - found another one too googling around - add 1st and last number 1+100 = 101 - ask yourself how many 'pairs' are between the 2 numbers (100/2) - there are 50 pairs - multiply that times 101 = 5050. . .

The other ways are cool too

Not china - rural south. . ., hard teacher.

Atleast we have some hope in our school system....although, I must admit I am surpised that this is in the south.

#### ed21x

##### Diamond Member
Originally posted by: Gibson486
Originally posted by: episodic
Thanks - found another one too googling around - add 1st and last number 1+100 = 101 - ask yourself how many 'pairs' are between the 2 numbers (100/2) - there are 50 pairs - multiply that times 101 = 5050. . .

The other ways are cool too

Not china - rural south. . ., hard teacher.

Atleast we have some hope in our school system....although, I must admit I am surpised that this is in the south.

the south certainly does better in schooling than such backwards school systems in california that somehow manages to be ranked below 47th every year.

#### SsupernovaE

##### Golden Member
I went to high school in the South. Richmond, VA. Although, it was one of the best public schools in the country.

#### HaxorNubcake

##### Golden Member
Gauss figured it out himself in primary school. wtf is wrong with you?! :|