Brainteasers

Puzzles to test mathematical skills, set by Anita Straker. Solutions below More brainteasers on www.tes.co.ukteacherbrainteasers

Emergency call

Using just three 9s, and any of the symbols +, - , X, V and C, make the following numbers: a. 1 b. 2 c. 3 d. 4 e. 8 f. 9 g. 11

Tomato soup

48 tins of tomato soup were packed side by side in a rectangular box so that they just fitted.

Show how to rearrange the contents so that 50 of the same tins of soup can be fitted into the same box.

SOLUTIONS Tomato soup (ages 14-16) When they are side by side, 8 columns of 6 tins can be fitted in. The width of the box is 16r, where r is the radius of the tin. When staggered as shown, 9 columns can be fitted in, 5 columns of 6 tins and 4 columns of 5 tins (50 tins). ABC is an equilateral triangle, so BD = 2r sin 60o = rC3. The width needed is 2r + 8rC3 = 15.86r to 2dp. They will therefore fit in the box of width 16r.

Emergency call (ages 9 to 13) Possible solutions are: a. C9 X C9 V 9 = 1; b. C9-(9 V 92; c. C9 X (9 V 93; d. C9 + (9 V 94; e. 9 - (9 V 9) 8; f. (9 V 9) X 9 = 9; g.99V9=11.

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