mental math

Algebra Level 1

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 = ? \large{1+2+3+4+5+6+7+8=?}


The answer is 36.

A Former Brilliant Member by A Former Brilliant Member

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3 solutions

Aaryan Maheshwari
Sep 26, 2017

Zum of first n natural numbers=[n(n+1)]\2

Here,n=8 so [n(n+1)]\2=[8(9)]\2=36

3 Helpful 0 Interesting 0 Brilliant 0 Confused
Munem Shahriar
Sep 26, 2017

n ( n + 1 ) 2 \dfrac{n(n+1)}{2}

8 ( 8 + 1 ) 2 \dfrac{8(8+1)}{2}

72 2 \dfrac{72}{2}

= 36 =\boxed{36}

2 Helpful 0 Interesting 0 Brilliant 0 Confused
Robin Ender
May 25, 2018

(1+8) 8/2=9 8/2=72/2=36

0 Helpful 0 Interesting 0 Brilliant 0 Confused

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