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Problem

When travelling by aircraft, passengers have a maximum allowable weight for their luggage. They are then charged £10 for every kilogram overweight. If a passenger carrying 40 kg of luggage is charged £50, how much would a passenger carrying 80 kg be charged?

Solution

A £50 charge represents 5 kg overweight (5 £10 = £50).
So 40 5 = 35 kg must be the maximum allowable weight for baggage.

Hence 80 kg is 80 35 = 45 kg overweight and the passenger would be charged 45 × £10 = £450.

Can you find a formula to calculate the charge for a given weight of baggage, W kg?
What would your formula produce if W = 30 kg?