Agrocery store has a shelf with half-gallon containers of milk. what type of number best represents the total number of gallons? you the choices are
real number , rational number, irrational number, integer, and whole number

As a number, half-gallon can be represented as 0.5.
In order to answer this question we will define each term:

whole numbers are numbers that can be defined as a number without fractions which are greater or equal than 0. E.g. 2 0 1 5 6 85

integer numbers are numbers that can be defined as a number without fractions but which can be either equal to 0 or greater and lower than 0
E.g. -9 -68 8 0 59

rational numbers are  any number that can be expressed as a fraction p/q of two integers E.g. 0.5 = 1/2 1 = 1/1 1.25 = 5/4

irrational numbers are those which have an approximate value E.g. pi = 3.14...
√2 = 1.41

real numbers are all of the above

From all those kind of choices the most accurate representation is rational numbers.