Losing weight

This puzzle is based on one used by Mensa, the high IQ society, in its IQ tests. This one's not particularly tough, but it is nicely confusing. Don't let a little confusion discourage you!

The puzzle

If seven footballers can lose a total of 10kg in weight in 8 hours of training, how many more footballers would be needed to lose a total of 10kg in only 4 hours of training provided the new footballers shed weight only half as fast as the original seven.

The solution

In 4 hours the existing seven footballers will lose 5kg. So the extra footballers will need to shed an additional 5kg. The extra footballers only shed weight at half the rate of the exisiting ones, so twice as many will be needed to lose the required 5kg. So fourteen more footballers are needed.

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