Analysis: This question examines the application of division. The number of girls is a multiple of that of boys. According to the topic, there are 7 boys, 2 girls1,and the number of girls/boys is the required result.
The problem solving process is as follows:
Solution: 2 1÷7=3
A: The number of girls is three times that of boys, which is judged by calculation.
The nature of the division operation:
1. If a number is divided by (or multiplied by) a number and then multiplied by (or divided by) the same number, the number remains the same. For example: 68÷ 17× 17=68 (or 68× 17÷ 17=68).
2. A number divided by the product of several numbers can be divided by the factors in the product in turn. For example: 320÷(2×5×8)=320÷2÷5÷8=4.
3. The quotient of a number divided by two numbers is equal to the number divided by the dividend in the quotient, and then multiplied by the divisor in the quotient. For example: 56÷(8÷4)=56÷8×4=28.
If the product of several numbers is divided by a number, any factor in the product can be divided by this number and then multiplied by other factors. For example: 8×72×4÷9 = 72÷9×8×4 = 256.
When the sum of several numbers is divided by a number, you can divide each addend by this number first, and then add each quotient. For example: (24+32+16) ÷ 4 = 24 ÷ 4+32 ÷ 4+16 ÷ 4 =18.
6. If the difference between two numbers is divided by a number, the quotient obtained by dividing the minuend by this number can be subtracted from the quotient obtained by dividing the minuend by this number. Example: (65-39) ÷13 = 65 ÷13-39 ÷13 = 2.