Good morning class. Today we are going to look at percentages. A percentage is a fraction – Jones, stop picking your nose and flicking it at Davis – I'm sure he doesn't like it, do you Davis? – Oh, very well, carry on.
So a percentage is like a fraction. To demonstrate, we will take the example of a wallaby and a cow – No, Jones, I did not mean the headmistress.
Suppose a wallaby turns 1% of its food into methane, while the cow turns 10% into methane. The cow produces considerably more methane than the wallaby, but you might expect that because the cow is much bigger and bulkier than the wallaby – Thank you Jones, I am not saying the headmistress is fat. – The pies have nothing to do with it; she has a thyroid condition. – No, Davis does not have a thyroid condition, do you Davis? – Oh, very well, carry on.
So the cow emits more methane because it is bigger and eats more food. But consider a giant wallaby, five times the size of a cow JONES GET DOWN FROM THERE – I did NOT ask you to portray a giant wallaby, merely to consider one. – I am perfectly aware that visual metaphors are a useful reinforcement to the educational process. – So if you are a giant wallaby, where is the cow for comparison? – What was that, Davis? – Oh, very well, carry on.
So, Jones is portraying our giant wallaby – No Jones, not Wallzilla, just an ordinary giant wallaby. – No you cannot breathe fire. – I am aware that methane is flammable but you do not have a lighter. – Give that here! You can't use it anyway: you are a wallaby and lack opposable thumbs. Ha!
Anyway, Jones is a giant wallaby and Davis is now a comparatively small cow, a fifth the size. As Jones is much bigger than Davis we might expect him to emit more methane, around five times as much as the cow. However, because wallabies emit a much lower *percentage* of methane (1% rather than 10%), the giant wallaby would emit 1/10th of a cow of equivalent size. Assuming a normal sized cow emits 1 standard cow unit (SCU) of methane, a cow-sized wallaby would emit 1/10th of an SCU. As Jones is five times the size of Davis – no, Jones, I'm not saying that you are fat – he will emit 5/10ths of an SCU, or around half the methane of the much smaller cow.
COWARD! COWARD! WAKE UP! Have you heard a word I've said? – I mean about percentages! Hold on a minute – JONES, STOP TRYING TO LIGHT DAVIS'S FARTS!