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97×96=(100−3)(100−4) · every mental math trick is a cleverly-cut rectangle · runs locally
97×96 (near 100)
12×13 (near 10)
998×997 (near 1000)
47×43 (near 50)
step 1
step 2
step 3
step 4
⊞
97×96 = (100-3)(100-4) = 100²+100×-3+100×-4+-3×-4 = 10000+-300+-400+12 = 9312
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