Fiddly fractions in #MondayMaths

Blog: Vicki Robinson , Communications Officer | Posted: 30/08/16
Fiddly fractions in #MondayMaths

A clue for this week’s #MondayMaths problem is the fictional idea of Platform 9 and ¾ at London’s Kings Cross (but we’re taking the concept of fractional train platforms much more literally!)

Year 8 students following our mastery curriculum will work on addition and subtraction of fractions this coming term. This is a great puzzle to put these skills into practice, as it challenges students to:

  • Identify the carriage lengths as fractions (the train lengths are all the same, but they each have a different numbers of carriages – this means the carriages are all different fractions of one whole train length)
  • Add together fractions of different denominators
  • Decide the best way to express the answer

A few clues

Because all the trains are the same length, it should become clear that this is an ‘addition of fractions’ problem – as we’re asking how to add together the lengths of carriages from each train, with each carriage measuring a fraction of a full train length.

As the diagram shows where the carriages line up (shown by the dotted lines), students can begin to spot which fractions they should be adding up.

MM 43q b

Once students’ reach this point, it’s simply a matter of using their understanding of adding fractions to find the full length of the platform in fractional form.

Breaking it down

When covering additions of fractions, we’d normally look at two different denominators instead of three, and so this may prompt some questions from your class about the best way to present the answer.

It might be a good idea to calculate the fractional addition in two stages as finding a common denominator of three fractions can be quite tricky.

Students can decide if they want to find a common denominator for all three or work it out by adding the fractions in stages.

And remember, the final solution doesn’t simplify easily. It’s your choice whether to express the answer in mixed or improper fractions.

Our workings out will be shared on Thursday. Tweet us to let us know how you got on!

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