Brainteasers

18th June 2004 at 01:00
Puzzles to test mathematical skills, set by Anita Straker. Solutions below More brainteasers on www.tes.co.ukteacherbrainteasers

Age 7-11. pt = Say it with flowers

In a bunch of 24 flowers, there are 17 roses and 9 yellow flowers.

What is the smallest number of roses that could be yellow? Age 9-13. Descending numbers

Descending numbers are whole numbers such that each digit is different and smaller than the one before.

92 is a two-digit descending number.

863 is a three-digit descending number.

9754 is a four-digit descending number.

How many three-digit descending numbers are there?

SOLUTIONS Say it with flowers The smallest possible number of yellow roses is 2. Since there are 17 roses in the bunch, there are 7 other flowers.

Assume all the other flowers are yellow, and there are 9 yellow flowers altogether, then 2 of the roses are yellow. Descending numbers There are 120 three-digit descending numbers: 1 betweeen 200 and 300 (210); 3 between 300 and 400 (321, 320, 310); 6 between 400 and 500 (432, 431, 430, 421, 420, 410); 10 between 500 and 600; 15 between 600 and 700; 21 between 700 and 800; 28 between 800 and 900; 36 between 900 and 1,000.

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