Saturday, January 9, 2010

Long division

I was in Vancouver when a construction guy asked a question similar to "what is 1200 divided by 15" it was 5 am so I pretty much ignored the question. But it got me thinking.

"15 times 100 is 1500, so the answer is less than 100"

"1500/2 is 750 so the answert is more than 50"

"750+750/2 is 1125, so the answer is slightly more than 75"

"1200-1125 is 75, 5 times 15 is 75, so add 5 to 75 and the answer is 80."

I checked the calculator, sure enough. I can do long division in my head! I tried more obscure problems and the same technique works, the only hard parts being mistakes in addition, and converting remainders into decimals. My accuracy rate is only about 75% and it takes a minute or two, but I can do it. I don't know why this surprised me as much as it did. Long division has always been something I relied on calculators to do. But it is pretty clear that a few weeks of practice and I could spit out answers almost as quickly in my head.

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