I'll try to explain, by showing a similar example.
Write an expression for the number of gallons represented by c cups. Use multiplication by a fraction. Substitute 12 1/2 cups into your expression.
There are 16 cups in one gallon (US liquid measurements). This means that one cup is 1/16th of a gallon.
Let c = the number of cups
Then, equal number of gallons is (1/16)c
The expression (1/16)c shows "multiplication by a fraction", so this expression satisfies the first requirement.
Next, we are told to substitute the given number of cups for symbol c in our expression, followed by doing the arithmetic to find out the equivalent number of gallons.
The given number of cups is a mixed number: 12 1/2. In algebra, we do not do arithmetic with mixed numbers; we convert them to improper fractions first.
12 1/2 = 25/2
(1/16)(25/2) = 25/32
12 1/2 cups = 25/32 gallons
Your questions? :cool:
PS: In the US, three teaspoons make 1 tablespoon; in the UK, four teaspoons make 1 tablespoon