The numbers 1, 2, 3,... Are written on the blackboard , 2009, arbitrarily erase two numbers a and B, and then rewrite them as the difference between the two numbers, so continue until If there is only one number left, is the last number left odd or even?

The numbers 1, 2, 3,... Are written on the blackboard , 2009, arbitrarily erase two numbers a and B, and then rewrite them as the difference between the two numbers, so continue until If there is only one number left, is the last number left odd or even?

impossible
1. If two even numbers are erased, the sum or difference of the numbers is still even, and the new array is still odd;
2. If two odd numbers are erased, the sum or difference of the numbers is even, and the new array is still odd;
3. If an even number and an odd number are erased, the sum or difference of the number is odd, and the new array is still odd
So the final number must be odd. It won't be even
Bow! Give me some points ~!

Calculation: 0.9999 × 1.3-1.111 × 0.17

0.9999×1.3－1.111×0.17 =0.9999X1.3-（0.1111X1.7）=9X0.1111X1.3-（0.1111X1.7）
=0.1111X(1.3X9-1.7)
=0.1111X10
=1.111

2+4+6+8+10+12+14+16+18=______ ×______ ．

2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18, = (2 + 18) × 9 / 2, = 20 × 9 / 2, = 10 × 9