In fact, this sentence is wrong: "I have 10 yuan left, and I owe my father 490 yuan and my mother 490 yuan". 970 divided by 2 equals 485, plus 10 yuan, I owe 495 yuan, not 490 yuan.
Or how about this: I bought a pair of leather shoes and spent 970 yuan. I paid back 20 yuan, 970+20=990 (not 490 respectively, but 990 respectively), and then added my own 10, which was equal to 1000. This kind of problem belongs to a kind of thinking illusion, and it will come out in the future.
Extended data:
Definition theorem formula
1. additive commutative law: Two numbers are added to exchange the position of addend, and the sum is unchanged.
2. The law of addition and association: When three numbers are added, the first two numbers are added first, or the last two numbers are added first, and then the third number is added, and the sum remains unchanged.
3. Multiplication and exchange law: when two numbers are multiplied, the position of the exchange factor remains unchanged.
4. Multiplication and association law: When three numbers are multiplied, the first two numbers are multiplied, or the second two numbers are multiplied first, and then the third number is multiplied, and the product remains unchanged.
5. Multiplication and distribution law: When two numbers are multiplied by the same number, you can multiply the two addends by this number respectively, and then add the two products, and the result remains unchanged. Such as: (2+4)×5=2×5+4×5.
6. Nature of division: In division, the dividend and divisor are expanded (or reduced) by the same multiple at the same time, and the quotient remains unchanged. Divide 0 by any number other than 0 to get 0.
7. Equation: An equation in which the value on the left of the equal sign equals the value on the right of the equal sign is called an equation. Basic properties of the equation: When both sides of the equation are multiplied (or divided) by the same number at the same time, the equation is still valid.
8. Equations: Equations with unknowns are called equations.
9. One-dimensional linear equation: An equation with an unknown number of 1 is called a one-dimensional linear equation. Example method and calculation of learning linear equation of one variable. That is, an example is given to illustrate that the formula is replaced by χ and calculated.
10. Score: divide the unit "1" into several parts on average, and the number representing such a part or points is called a score.
1 1. Addition and subtraction of fractions: add and subtract fractions with denominator, only add and subtract numerators, and the denominator remains unchanged. Fractions of different denominators are added and subtracted, first divided, then added and subtracted.
Baidu encyclopedia-primary school mathematics