Magazine article Times Educational Supplement

# Maths - Pivotal Precision: Resources

Magazine article Times Educational Supplement

# Maths - Pivotal Precision: Resources

## Article excerpt

A maths teacher's tombstone should read something like this: "J.G. died after 79.1 years (3sf)". Most of our waking lives, after all, are spent telling our students to round that final answer to some suitable level of precision, and "three significant figures" is often our mantra. And yet we have all seen workings where the precision is to 3sf, only for the answer to be given to 5sf.

Perhaps the best way to get our young disciples to take sensible precision on board is to show them an example where things go wrong. A student of mine (let's call him John) once produced the following. John's starting question was "Find the angle between the vectors and ." He began promisingly:

John has dutifully followed what he believes the 3sf rule to be, working to this precision as he goes along. Apart from this, his method is fine. He continues:

When I present this to my A2 group, they follow with interest. "He should be giving more accuracy in his working, but he can't be that much out," says Rachel, and this is the general view.

But when they work out the percentage error they discover he is 20 per cent out. …

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