Скачать или смотреть The Two Hardest Two-Digit Numbers to Multiply

Picking up on a series I started a couple summers ago, if we're multiplying in our head, no calculator, what are the two hardest two-digit numbers to multiply together? That is, what pair of numbers would be best at preventing us from using some clever trick to speed up our calculation?

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On one level, this depends a lot on whether we happen to know certain number tricks. But that doesn't mean this is entirely subjective. For example, we'll definitely want to avoid certain numbers that factor in several different ways, because that increases the number of options we have for manipulation. In today's example, 37×72, the fact that 72 has so many different factors allows us to manipulate the problem and end up with the considerably easier computation of 111×24. From there we use something called the 111 trick, though we could probably also turn it into some basic distribution and achieve the same result.

#mentalcalculation #mathtricks #multiplicationtips

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