Sometimes, we may not have all the ingredients to make a recipe, but we may have something we can fittingly substitute.  How does this affect the measurement amounts in the recipe?  For example, let’s imagine we are making Rice Krispie cake.  The recipe calls for 32 large marshmallows, but we only have miniature marshmallows.  We can still use the small marshmallows, but we will need to estimate how many mini marshmallows would make one large marshmallow, and multiply that number by 32. 

What if you want to spice up your chocolate chip cookies by adding almonds and coconut?  Your recipe calls for 2 cups of chocolate chips, but you want to add 1/3 cup of almonds and 1/6 cup of coconut.  How much chocolate chips do you still have to add?  Well, we simply need to subtract, using fractions.

We still need to add 1 and ½ cups of chocolate chips.  It is important to remember that when adding and subtracting fractions, we need to use a common denominator.