Question 923653
Suppose you have:
{{{ 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 }}}
The sum is {{{ 55 }}}
The formula for this is:
{{{ S = ( n*( n+1 ) ) / 2 }}}
where {{{ n }}} is the last number
check:
{{{ 55 = ( 10*11 ) / 2 }}}
{{{ 55 = 110/2 }}}
{{{ 55= 55 }}}
OK
Now use it for numbers 1 to 100
{{{ S = ( 100*101)/2 }}}
{{{ S = 10100/2 }}}
{{{ S = 5050  }}}