When rounding any number that is 5 or above we round up, any number that is 4 or below we round down. After we round all number that are behind the rounded number turn to 0. So because 8 is greater then 5 we round up, and because we are rounding to the tenths place the "8" turns into a 9 like so. Making are new number 4.9.
Hope this helps!=)