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Dividing common fractions by whole numbers

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

  1. WolfPaul

    WolfPaul Occasional 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. teacup71

    teacup71 Occasional 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_Ulam

    Vince_Ulam Star 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. nick909

    nick909 Star 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. star9

    star9 New 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.
     

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