We use the decimal system, which means every place you "move" in a decimal number, we multiply or divide by ten. We have the unit on the left side of the dot, and the tenth 1 place to right of the dot, the hundredth 2 places to the right of the dot. In math terms, let's use the famous number pi as an example.
[tex]3.14159265359\ldots=3+\frac{1}{10}+\frac{4}{100}+\frac{1}{1000}+\frac{5}{10000}+\frac{9}{100000}+\cdots[/tex]A mixed number is a combination of the unit and the fractional parts of a number. For our number 4.29, we have 4 units and 29 hundredths, which means we can rewrite as:
[tex]4.29=\frac{429}{100}=4\frac{29}{100}[/tex]