Law: exchange the position product of two factors unchanged, and bargain the multiplication exchange rate. aXb=bxa
The first two numbers, or the first two numbers multiplied by the last two numbers, have the same product, which is called the law of multiplicative association (axb)xc=ax(bxc).
Multiply the sum of two numbers by one. You can multiply this number separately and then add it up. ax(b+c)=axb+axc
The fourth unit is about the meaning and nature of decimals.
There are two ways to read decimals: one is to read fractions, and the whole part with decimals is to read integers; small
The digital part is read by fractions. For example, 0.38 is pronounced as 38%, and 14.56 is pronounced as 14 and 56%. In another way, the integer part is still read as an integer, the decimal point is read as a "dot", and the decimal part reads the numbers on each digit in sequence. For example, 0.45 is read as 0.45; 56.032 is pronounced as 56.032.
The comparison method of decimal size is basically the same as that of integer, that is, the numbers on the same digit are compared in turn from the high position.
Therefore, to compare the sizes of two decimals, first look at their integer parts, and the larger the integer part, the larger the number; If the integer parts are the same, the one with the largest number in the tenth place is larger; If the deciles are the same, the percentile is larger;
Properties of decimals: ① Add or remove zero at the end of decimals, and the size of decimals remains unchanged.
For example; 2.4 = 2.400, 0.060 = 0.06.② When the decimal point is shifted to the right by one, two and three places respectively, the decimal size will change, and the decimal value will be enlarged by 10 times, 1000 times and1000 times respectively. ...
Times; If the decimal point is shifted to the left by one place, two places and three places respectively, the decimal value will be reduced by 10 times, 100 times and 1000 times respectively. For example, expand 7.4 10 times to be 74, and expand 100 times to be 740. ..