1) 1+2+3+4...+1000
You add one number with another number which will make 1000.
1+999=1000
2+998=1000
Ect.
Then add all the 1000's up and you will get 501 1000's therefore 1000*501=501000
2) You would gain 1%(to find 1 percent time the number of dollars($501000 dependable value) by 0.01 and add on to the value) per however long the period of time is
3) There is no difference apart from the percentage at the end of 2)