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Wednesday, March 13, 2013

Probability, Percentages and the Eleven Plus

It has been known, we understand, for parents to compare schools when talking about eleven plus passes. “Oh, dear! School A only had eleven Eleven Plus passes this year. I am glad my child is not there!”

This could be a little misleading! School A may only have had fifteen true eleven plus candidates so for eleven children to pass could be considered to be wonderful.  This could be 73.33%! (How one has 0.33 of a candidate is rather hard to imagine!)

School B, however, may have had far more passes – but may have entered a lot more children. Twenty children passing out of seventy five gives 26.66 per cent. We could of course round the 0.66 up to a whole number suggesting 27 per cent of children passed.

Some parents may feel a need to be a little conservative about accepting the percentages – without knowledge of the actual numbers involved.

It may be a little more accurate to talk about the proportions of children passing. Some eleven plus children will know that the probability of getting a six is one chance in six.

Eleven Plus Question

What is the probability of a child in School A achieving a place in a grammar school?

What is the probability of a child in School B being offered a place?

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