Leave it all in terms of Pi until the last minute

Pi number

Pi number (Photo credit: J.Gabás Esteban)

Today I heard this golden nugget of advice from the most talented maths teacher I’ve ever met…

When teaching students to do calculations involving Pi, leave it all in terms of Pi until the very last minute.

Rather than the workings for volume of a cylinder of radius 10cm and height 20cm being:

Pi X 10^2 = 314.159…

314.159… X 20 = 6283.2… cm^2

Instead simplify first, leaving in terms of Pi:

Pi X 10^2 = 100Pi

100Pi X 20 = 2000Pi

2000Pi = 6283.2 cm^2


  • It teaches them how to leave answers in terms of pi without an extra lesson on it
  • It avoids the messy writing out of irrational decimals mid-calculation (which avoids the possibility students committing the ultimate sin of rounding mid-calculation)

Made my day 🙂

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1 Response

  1. 19/03/2014

    […] via Leave it all in terms of Pi until the last minute | Great Maths Teaching Ideas. […]

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