If you read the decimal version of 4.8 out loud, it should be "four and eight-tenths." This will always give you a good place to start when changing a decimal into an equivalent fraction.
Now, this is a mixed number: 4 and 8/10. To further simplify it as a mixed number, we can leave the 4 alone and reduce the fraction (8/10). Both the numerator and denominator are divisible by 2, so we can conclude (8/10) = (4/5). A correct answer in mixed number form is 4 and (4/5).
However, to change 4 and (4/5) to a single (improper) fraction, you first multiply the denominator (5) by the large number out front on the left (4) and ADD this product to the numerator (4). This number is your new numerator and it will still have the same denominator as before.
Here, 4 and (4/5) = [(5)*(4) + 4]/5 = (20+4)/5 = 24/5.
24 and 5 have no common factors, so this fraction is already in reduced form.
4.8 = 4 8/10 = 4 4/5