Question 1206526
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These are all examples of a strategy for mental calculations based on the pattern (A+B)(A-B)=A^2-B^2<br>
17*23 = (20-3)(20+3) = 20^2-3^2 = 400-9<br>
23*37 = (30-7)(30+7) = 30^2-7^2 = 900-49<br>
18*30 = (24-6)(24+6) = 576-36 = 540<br>
While that strategy can of course be used on the last example, it is not a good place to use it, since 18*30 is much more easily calculated as 18*3*10.<br>