01+2+3+4+5+.........100(100 terms)
it can be seen as follows:
1+2+3+4+5+.......+95+96+97+98+99+100
can be rewritten as follows:
(1+100)+(2+99)+(3+98)+(4+97)+(5+96)........so on
every term become 101 this way and the number of such terms will be half as it was before
so before it was 100 terms, now it is 50 terms.
101+101+101+101+101+.......added 50 times
which is 101*50=5050
