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Say a friend agrees to square my pocket change, I have 10 x 10p coins = £1.

He gives me 100 x 10p coins, I have £10

Next day I have 100 x 1p coins also = £1, he gives me 100 x 100 x 1p = £100 Why ?

xatabay
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  • Indeed, I have no idea why anybody would square your pocket change (i.e., square the number of coins of a certain value). Can I have his address? – Hagen von Eitzen Feb 06 '15 at 19:18
  • Not only that, but you are getting a great exchange rate. When I last spent British coinage, I could only get 1 shilling for 12 pence and one pound for 20 shillings -- 240 pence per pound. – Mark Fischler Feb 06 '15 at 19:22

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The idea is the "square" is units dependent.

If your friend agrees to double the amount of money in your pocket, it doesn't matter what units are being used. Double of 1 pound is 2 pounds, double of 100 pence is 200 pence. The factor of $2$ has no units attached.

On the other hand, if your friend decides to "subtract 2" from the money in your pocket, units make a big difference. Starting with 4 pounds would you end up with 2 pounds, or starting with 400 pence would you end up with 398 pence? Here "subtract 2" requires units to make sense.

In your example, changing units changes the outcome since you are failing to square the units. I don't know offhand what a square pound or a square penny is, though.

Umberto P.
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