# Dividing common fractions by whole numbers

Discussion in 'Primary' started by WolfPaul, Nov 15, 2015.

1. ### WolfPaulOccasional commenter

Hi despite many years teaching Y6 haven't done this before! I can't make up my mind which approach. Either:

a) Change the fraction into an equivalent with a numerator that divides by by the divisor, eg

3/4 ÷ 2 = 6/8 ÷ 2 = 3/8

or just to go for multiplying the denominator, eg

b) 3/4 ÷ 2 = 3/4x2 = 3/8

Would try both but think this probably = confusion!

Any thoughts?

2. ### teacup71Occasional commenter

I think this is down to what we mean by maths mastery. The understanding of maths. So both methods lead to more understanding. So far I have been doing 'entering' with the majority of the children so I have just taught multiplying by finding the reciprocal- am I using the correct term? Flipping the second fraction.
This looks like an easy method but the mathematical understanding goes deeper. So I think this is why it is not on the expected progress seen in the test framework.

Last edited: Nov 15, 2015
3. ### Vince_UlamStar commenter

@WolfPaul

Go with b but make it easier on yourself. It's the same rule as dividing by fractions: Invert the divisor integer, 2, so that you have it's reciprocal, 1/2, and then multiply across, 3/4 * 1/2 = 3/8. Remember the rule; invert & multiply.

4. ### nick909Star commenter

Hi WolfPaul, I've yet to teach this as well (a week or two yet) but I think I'll be going for b). With some visual/physical resources at first to illustrate the process. b) is the easier of the two to do.

5. ### star9New commenter

b is incorrect.

It should be

3/4 ÷ 2 = 3/4x1/2 = 3/8

You need to do a to get the understanding. If you want half of a fraction it is easy if the numerator is an even number. If not, you need to divide your shape into more pieces - double the denominator - find an equivalent fraction with an even numerator.

b shows that ÷ 2 is finding half of something.

If you just teach b you are not teaching the understanding, just the method.