分数：fractions
分子：numerator
分母：denominator
分数的加减乘除：addition，subtraction，multiplication and division of fractions
繁分数和假分数：mixed number and improper fraction
繁分数是指一个数由一个整数和一个分数构成。
假分数是指分子大于分母的分数。例如：7/3
小数：decimals
科学计数法：scientific notation
Sometimes decimals are expressed as the product of a number with only one digit to the left of the decimal point and a power of 10. This is called scientific notation. For example, 231 can be written as 2.31×102 and 0.0231 can be written as 2.31×10-2. When a number is expressed in scientific notation, the exponent of the 10 indicates the number of places that the decimal point is to be moved in the number that is to be multiplied by a power of 10 in order to obtain the product. The decimal point is moved to the right if the exponent is positive and to the left if the exponent is negative. For example, 20.13×103 is equal to 20,130 and 1.91×10-4 is equal to 0.000191.
