I comes from numero, the ablative form of the Latin word numerus.
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In principle, you can count backwards; or use some shortcut (such as calculating the number of days, dividing by 7, and obtaining the remainder).
Powers are a convenient shortcut for repeated multiplication.
the shortcut way of dividing is mutiplying
The multiple of ten can be reduced to the smaller number by moving the decimal place of the numerator one place to the left. However, this may only be a marginal short cut. For example, dividing 1256 by 3450 is equivalent to dividing 125.6 by 345 but that is hardly a shortcut!
You add two zeros at the end of the answer 80*90=7200