Explicație pas cu pas:
1+100=101
2+99=101
...........
50+51=101
101×50=5050
R:5050
B:1+2+3........+1000
1+1000=1001
2+999=1001
................
500+501=1001
1001×500=500500
R:5005000
C:101+102+103
.............+999+1000
1+2+3........+100
1+100=101
...........
50+51=101
101×50=5050
1+2+3.........+1000
1+1000=1001
2+999=1001
............
501+500=1001
1001×500=500500
500500-5050=495450