1〕756=2*2*3*3*3*7=27*28

2] In order to maximize the product, three numbers must be the closest. 5 1/3= 17。 So these three numbers must be 1 1,17,23.

The composite number of 3] 1 to 30 is 4, 6, 8, 9, 10, 12, 14, 15, 16, 18. The two biggest differences are 4 and 27.

4] 144 = 2 * 2 * 3 * 2 * 2 * 3, where two combinations of prime numbers can only be 16 and 9.

5〕 10 * 10 & lt； 107， 1 1 * 1 1 & gt； 107, and then use 1 to try the quotient and find that it is a number; 26 * 26 & lt703, * 27 & gt703, and then use 1 to 26 to try to find 703 = 19 * 37.

6] This question is wrong, because one of the three consecutive natural numbers must be divisible by 3, but 1729 cannot be divisible by 3.

7] Because the remainder of 7599 divided by a certain number is 9, 7590 can be divisible by a certain number. 7590 = 2 * 5 * 3 * 1 1 * 23, so the minimum number is 1 1 (because the divisor must be greater than the remainder) and the maximum number is 23.

b grade

1] because 60 = 2 * 2 * 3 * 5 = 4 * 3 * 5 = 2 * 6 * 5 = 2 * 3 *10.

4+3+5= 12 2+6+5= 13 2+3+ 10= 15

So the fourth ring road is played by C.

2〕46=2*23, 2+23=25

3〕 1 170-78= 1092 1092=2*2*3*7* 13

Since this two-digit number is greater than 78 and less than 100, it can only be 84.

4] 63+91+129-25 = 258 258 = 2 * 3 * 43, so it can only be 43.

5) The sum of numbers divisible by 3 can also be divisible by 3, in which only four groups of 0 18, 918,078,978 can be formed, while two groups of 9 can form 12, and the group of 0 can form 8 and a * * 20.

6] are 7530 and 1035 respectively, and the total is 8565.

7] are 1047, 1074, 1407, 1470, 1704,

The fifth place is 1704.