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Which of the following is the best estimate for the length of a pen?
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A) Twelve kilometres, B) twelve centimetres, C) twelve millimetres, or D) twelve metres.
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Now all of these measurements have been given in the metric system and the metric system of length is based around the metre.
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And just to give you some idea, the average car is about one point four, one point five metres tall.
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Now let’s think about all these different units which have been defined as being multiples of a metre or fractions of a metre.
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A kilometre is a thousand metres.
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So twelve kilometres is twelve thousand metres.
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That’s thousands of times as tall as a car; that’s not a very good estimate for the length of a pen.
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Okay, how about twelve centimetres?
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Well, one centimetre is a hundredth of a metre.
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There’re a hundred centimetres in a metre.
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So twelve centimetres is twelve hundredths of a metre, which is about a tenth of a metre.
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And on our car that would be about the width of a headlight, which seems like a reasonable estimate for the length of a pen.
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Let’s think about twelve millimetres.
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One millimetre is a thousandth of a metre.
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And that means that one centimetre has ten millimetres in it.
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So twelve millimetres is gonna be a tenth the size of twelve centimetres.
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And that’s probably about the width of a bulb from a headlight.
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Well that’s pretty small for a pen.
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So that’s probably not the right answer.
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And then lastly, we need to consider metres.
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Remember we said the height of an average car is about one point five metres.
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So twelve metres is about the height of eight average cars stacked on top of each other.
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Now that’ll be a very long pen.
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So that’s probably not a very good estimate either.
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So it looks like our answer is B, twelve centimetres.
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So the answer then, the best estimate for a pen from that list is about twelve centimetres.