Analysis: 1 is neither a prime number nor a composite number. So 20-8- 1= 1 1.

2. The greatest common divisor of m and n (C)

Analysis: Because B and C are not 2, 3 and 5, there can be no divisor other than 1 between the two numbers, so the greatest common divisor is 1.

Step 3 fill in the blanks

The greatest common divisor of 1)24 and 56 is less than their least common multiple ()

Analysis: The greatest common divisor of 24 and 56 is 8 and the least common multiple is 168, so their greatest common divisor is less than their least common multiple 160.

2) A and B are both natural numbers. If a is divided by b= 12, then the least common multiple of a and b is (a) and the greatest common divisor is (b).

Analysis: If the larger number of two natural numbers is a multiple of the smaller number, the larger number is their least common multiple and the smaller number is their greatest common factor.

3) A, B and C are the smallest natural number, the smallest prime number and the smallest composite number respectively, so the square of A+the square of B+the square of C =( 20).

Analysis: The smallest natural number is 0, the smallest prime number is 2, and the smallest composite number is 4, so the square of A+the square of B+the square of C = the square of 0+the square of 2+the square of 4 =20.

4) A number consisting of six numbers, the highest bit is the largest prime number, the tenth bit is an odd number divisible by 5, the lowest percentile is the smallest odd number, and all other numbers are zero. This number is written as ().

Analysis: A number consisting of six numbers, so each number is a number, the largest prime number is 7, the odd number divisible by 5 in the tenth place is 5, and the smallest odd number in the lowest percentile is 1. Because the lowest percentile is the lowest percentile, this number has two decimal places and four integers. That is, the sum unit is 0, so this number is: 7000.438+0.