Hi, I'm Mandy Schall, math specialist Allegany County Public Schools. Today,
I'm going to model subtraction of fractions using a number line.
Today's problem is Albert is making punch for his birthday party. The recipe calls for one and three-fourths
gallons of ginger ale. He already had seven eighths of a gallon.
How much more ginger ale does he need to make the punch?
I know that I will be subtracting because I need to find out how much more is needed.
I will first write an equation to represent the problem.
One and three-fourths minus
seven eighths equals my unknown.
I know that 3/4 is equivalent to six eighths.
To make this problem easier I will name
one and three-fourths as
one and six eighths. I'm going to label my number line from zero
to one and six eighths.
I know that eight eighths is the same as one whole.
So I will label one on my number line.
I will now continue to label my number line
until I land on one and six eighths.
To subtract
7/8 from 1 and 6/8 I will start at 1 and
6/8 on my number line and I will hop back
seven times. Since each hop
represents 1/8
I land on 7/8.
I will now finish my equation.
1 and 3/4 minus 7/8
equals
7/8.
Albert still needs 7/8 of a gallon of ginger ale to make the punch.
