## Monday, August 10, 2009

### An Eleven Plus Average

You have just moved to a new five bed roomed house. There is a large conservatory – big enough to hold a table tennis table. You buy the table on line and it delivered the next day. You need some table tennis balls. You take the family to the large `Super Sport Shop’ and set out to purchase some ping pong balls.

A knowledgeable sales person comes up to you and asks if you need help. You admit your total ignorance and explain that you are grateful for any advice. The sales person assures you that new ping pong balls are very strong and can resist almost any pressure. “The balls will break at around eleven pounds of pressure.”

You dip your hand into a tub of balls and emerge with six balls selected at random. You then set out to test the strength of the balls. The balls break at different pressures:

9.5 8.0 11.0 11.5 9.6

Should you buy the balls from the tub?

When your eleven plus child has to read and reread a slightly confusing question like this you may feel that you are entitled to become frustrated if he or she does not appear to read the question carefully.

Your child will be able to work out the mean – or take the average. In this case the mean is 9.5. You know your children. Is this still a good buy?