1,2,3,4,6, 12

What are the natural numbers of 1-20 that are not even numbers?

9, 15

A number is a multiple of 15 and a factor of 30. This number may be (15,30).

Fill the brackets with different prime numbers:

15=(2)+( 13),27=(3)+(7)+( 17), 12=( 19)-(7),38=(3)+(5)*(7)

The greatest common factor of A and B is 1, and their least common multiple is (A*B).

Judge:

1. One of two adjacent natural numbers is always a multiple of 2. (× );

Now 0 is a natural number, right? Not 0 1.

If 0 doesn't count, that's right.

2. In a two-digit number, the maximum composite number is 9 times the minimum prime number. (√ )

Maximum total: 99

Minimum prime number: 1 1

99÷ 1 1=9

Multiple choice question:

The greatest common factor of two complex numbers is 1, and the least common multiple is 144. These two numbers are (b).

A. 1 and 144. B.9 and 16. C.8 and 18.

Application problem: 1. Xiaoming and Xiaogang began to do their homework at the same time. Xiaoming takes a 2-minute break in 8 minutes, and Xiaogang 12 takes a 2-minute break. How many minutes should they rest at the same time?

8+2= 10 minutes

12+2= 14 minutes

The least common multiple of 10 and 14 is 70.

At the same time, rest for at least 70-2=68 minutes.

There are a batch of bricks, 45cm long and 30cm wide. How many bricks does it take to lay a solid square?

The least common multiple of 45 and 30 is 90.

At least: (90÷45)×(90÷30)=6 pieces.

What are the natural numbers of 1-20 that are not even numbers?

9, 15