If it is a multiple of 3 or 5, it is a multiple of 15. There is 2000 15 = 133.

Then there are 666- 133 = 533 numbers that are multiples of 3 but not multiples of 5.

2. 1 1 1 1= 1 1* 10 1

Just decompose 1 1 into the sum of four numbers and multiply each number by 10 1.

For example: 303+505+ 10 1+202.

So the greatest common divisor should be 10 1.

Let this natural number be x.

Then (1997+x)/(2000+x) = 2000/2001.

The solution is x=4003.

4. Let the length of this sloping ground be x kilometers.

X/3.6+X/4.5= 1.8

5X+4X=32.4

9X=32.4

X=3.6

The length of this sloping ground is 3.6 kilometers.

5. Solution: Let the mass of water be 1,

The first time was 1/2 and the second time was1/2 * (1-1/3) =1/3.

The third time,1/3 * (1-kloc-0//4) =1/4, so the final alcohol is 3/4.

That's 75%.

6.2.7*34+ 15.4*34-8. 1*34=(2.7+ 15.4-8. 1)*34= 10*34=340