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Neurobics

Brain Exercises

Russell Dear

1. What is remarkable about the following statement?
Eleven plus two = twelve plus one.

2. Is the following statement true or false?
Most sons are first (i.e. eldest) sons.

3. True or false?
If you think of a whole number and multiply it by itself, then double the result and add 11, your answer will be a prime number (a prime is a number divisible exactly only by itself and one).

4. Find the next number in the sequence 0, 3, 8, 15, 24, ...

5. In a survey investigating children's understanding of probability nearly 3,000 eleven to sixteen year-olds were asked the following question:

A bag has in it some black and some white balls. A ball is chosen and its colour noted. After returning the ball, the bag is shaken. The process is repeated a total of four times, a black ball occurring on each occasion. A fifth ball is chosen.

What colour is it likely to be?

a) black is more likely again
b) black and white are equally likely
c) white is more likely this time.

Two-thirds of the young people thought b) was correct. The other choices had about equal support. What is the correct answer?

Answers in next month's issue.

Russell Dear is a Mathematician living in Invercargill