### Jan Nordgreen

Shared publicly -Probability to rescue

– How many girls are there in your class?

– I don’t know. But we are 10 boys.

– What do you mean you don’t know? Are you blind?

– I think I can help you though.

– If you would be so kind.

– I calculated that if two students from the class are selected at random to the School Council, the probability that both are boys is 0.15.

– There may be hope after all!

Problem source: UK Senior Mathematical Challenge, UK Mathematics Trust.

http://www.ukmt.org.uk/

Note: “Calculators, measuring instruments and squared paper are forbidden.”

– How many girls are there in your class?

– I don’t know. But we are 10 boys.

– What do you mean you don’t know? Are you blind?

– I think I can help you though.

– If you would be so kind.

– I calculated that if two students from the class are selected at random to the School Council, the probability that both are boys is 0.15.

– There may be hope after all!

Problem source: UK Senior Mathematical Challenge, UK Mathematics Trust.

http://www.ukmt.org.uk/

Note: “Calculators, measuring instruments and squared paper are forbidden.”

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