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$ \eqalign{\frac{2} {5} - \frac{1} {4} = \frac{8} {{20}} - \frac{5} {{20}} = \frac{3} {{20}}} $ |
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$ 22 \times 31 = \left( {20 + 2} \right)\left( {30 + 1} \right) = 600 + 20 \cdot 1 + 2 \cdot 30 + 2 = 682 $ |
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$ 92 \times 98 = \left( {100 - 8} \right)\left( {100 - 2} \right) = 10000 - 1000 + 16 = 9016 $ |