Question 568361
<pre>
Let the sum be S

 S =  1 +  2 +  3 + ... + 48 + 49 + 50   <-- there are 50 terms
 S = 50 + 49 + 48 + ... +  3 +  2 +  1   <-- there are 50 terms
  
add the two equations term by term:

 S =  1 +  2 +  3 + ... + 48 + 49 + 50   <-- there are 50 terms
 <u>S = 50 + 49 + 48 + ... +  3 +  2 +  1</u>   <-- there are 50 terms
2S = 51 + 51 + 51 + ... + 51 + 51 + 51   <-- there are 50 terms
2S = 51×50  <--51 times 50 because there are 50 51's added together                           
2S = 2550
 S = 1275 

Or by formula: {{{n(n+1)/2}}}

{{{50(50+1)/2}}} = 1275

Edwin</pre>