when you round you have to check the number to the right of the number you are rounding. If the number to the right is 0-4 then you keep the number the same. 5-9 the number you are rounding goes up by one. Now the 4 before the decimal point is in the ones spot. The 5 to the right of the 4 is the tenth spot and the 6 to the right of that is in the hundredth spot. so this is where we need to round. To the right of the 6 is a 4 so the number would stay the same. Now when you round you drop all the numbers after it so the number is 3184.56
