420024 Wrote:[Deleted because poster did not cite author.]
The sum of the consecutive integers from 100 to 150 can be written as
(100)+(100+1)+(100+2)....(100+50)
The sum of the consecutive integers from 125 to 150 can be written as
(125)+(125+1)+(125+2)...(125+5)
We know that the 125 is the same as (100+25) so when you subtract the terms you will cross out everything after this entry to see whats left.
(100+25)+(100+26)......(100+50) Subtract (125)+(125+1)....(125+25)
All that you will have left over is:
(100)+(100+1)+(100+2)....(100+24) because we crossed out everything equal to 125 and everything after it.
Therefore it is equal to the sum of the consecutive integers from 100 to 124.