Unit 6 · Topic 01 · Measurement
A carpenter's order slip said 2 m 45 cm of wood. The saw only understood centimetres.
Farhan, the carpenter's apprentice, had thirty seconds to convert it before the blade started.
Get the units wrong and the wood is cut short — or wasted.
Farhan was learning the trade in his uncle's workshop. The order slip read: '2 m 45 cm of teak for a shelf.' The saw's digital guide only accepted centimetres.
He typed 245. His uncle glanced over. "Check that."
Farhan re-read the slip. 2 m 45 cm — not 245 cm on its own, but two SEPARATE measurements that needed combining first.
"A metre is a hundred centimetres," his uncle said. "So two metres is two hundred centimetres. Add the forty-five on top."
200 + 45 = 245. Farhan's first typed number had actually been right, but only by accident — he'd guessed rather than converted.
His uncle set him a harder one to make sure it wasn't luck: 3.5 kg of nails needed splitting into small bags of 250 g each. "How many bags?"
Farhan started by converting the kilograms into grams. One kilogram is a thousand grams, so 3.5 kg is 3500 g.
3500 divided by 250. He worked it out: 14 bags exactly.
"Good. Now the one that catches everyone," said his uncle. He held up a paint tin: 2 L 350 ml, and asked how many 100 ml sample bottles could be filled.
Farhan converted: 2 L is 2000 ml, plus 350 ml is 2350 ml. Divided by 100, that's 23 bottles, with 50 ml left in the tin.
"You always do the same two things," his uncle said. "Convert to the smallest unit given in the problem, THEN calculate. Skip that first step and the numbers will be technically true and completely useless."
Farhan wrote the three conversion ladders on the back of his hand in pencil that day: 1 m = 100 cm, 1 kg = 1000 g, 1 L = 1000 ml. By the end of the week he didn't need to look at it.
The metric system is built entirely on tens, which is what makes it fast once you know the ladder: 1 km = 1000 m, 1 m = 100 cm, 1 cm = 10 mm. For mass: 1 kg = 1000 g. For capacity: 1 L = 1000 ml.
Converting to a SMALLER unit means MULTIPLYING (more of a smaller thing). Converting to a BIGGER unit means DIVIDING (fewer of a bigger thing).
A mixed measurement like 2 m 45 cm must be combined into ONE unit before any calculation — convert the larger part down and add the remainder, never treat the two numbers as already meaning the same thing.
The reliable method for any real problem: convert every measurement to the SAME, usually smallest, unit first, and only then add, subtract, multiply or divide.
Measure the length of three household objects with a ruler in centimetres, then convert each to metres.
Check a food packet's weight in grams and work out how many packets would make up 1 kg.
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