Division of Fractions by Whole Numbers and Fractions by Fractions

Before the Christmas break we were learning how to divide fractions by whole numbers (and by extension, divide fractions by fractions). I've always found that is much easier to teach this using models so that the kids understand the concepts before applying any rules or algorithms. Students and even teachers (some anyway) are familiar with using "Keep Change Flip" as a procedural method used to solve division with fractions, but don't truly understand why it works. As follows:

Given the following problem: Mr. E has ½ a bar of hersheys chocolate. He wants to split it equally between his three friends. How much chocolate will each friend get?

Chocolate bar before dividing equally between 3 friends (½)

 

Chocolate bar after dividing it equally between 3 friends (⅙)

Therefore:

From there, students develop the understanding that dividing is the same thing as multiplying by the reciprocal (For example: ½ ÷ 3 = ⅙, and can also be written as ½ × ⅓  which also equals ⅙).

Knowing that division is the same as multiplying by the reciprocal, you can easily divide fractions by fractions.

Example:  ½ ÷ ⅙ can be written as ½ ×  6/1 which = 6/2 which = 3.

Lastly, this also applies to whole numbers. Example:  
12 ÷ 4 = 3 
12 × 1/4 = 12/4 = 3


Wait!
If you have time, watch the video below of a student that has difficulty with the model (mainly due to a lack of conceptual knowledge of division) and my attempt (which I don't think was that great) at helping her solve the problem!

P.S. - Division of fractions by fractions can be modeled using fraction strips. I made a post prior to this where students were using them to solve word problems. It can be found here: Dividing Fractions by Fractions - Fraction Strips

A New Adventure~

Recently, I was accepted to the University of Delaware! I received notification that I was granted admission to the University of Delaware's graduate program of Education (PhD). I will obtain a PhD in Education with a specialization in Mathematics. This has some similarities to what I did in grad school for the M.S. in Ed. The main focus (or at least one of them) of the program is to examine critical issues of mathematics teaching and learning across K-12.

Continuing my studies was always lingering on my mind, and the opportunity to do is finally here. I still remember being 17 and getting accepted to Penn State, only to not be able to attend due to the cost of tuition. The University of Delaware offered to pay the entire tuition, in addition to offering a stipend, contingent upon teaching and doing research throughout my enrollment! Channeling my excitement and inner blue hen! 😊