The sum of 1~99 is 99*(99+ 1)/2=4950.

The sum of 1 to 30 1 is 301* (301+1)/2 = 45451.

The sum of 100 to 30 1 is 4545 1-4950=4050 1.

100~30 1 If the even sum is X, then the odd sum is X+1kloc-0/(* * 202 numbers, and the odd and even numbers are 10 1 respectively).

x+(x+ 10 1)= 4050 1

x=20200

That is, the sum of even numbers is 20200.

There seems to be something wrong with your answer.