Simple calculation of 6.4 × 4.5 + 3.6 × 45 I'm in a hurry

6.4×4.5+3.6×45
=0.64×45+3.6×45
=45×(0.64+3.6)
=45×4.24
=190.8

4 × 57.8 + 45.3 × 5.6 with simple calculation

=4.4×57.8+(57.8-12.5)×5.6
=4.4×57.8+5.6×57.8-12.5×5.6
=(4.4+5.6)×57.8-12.5×0.8×7
=10×57.8-10×7
=578-70
=508

0.4 * [5 / 6 * (3 / 20 + 0.45)] simple operation, how to calculate?

0.4*[5/6*(3/20+0.45)]
=0.4*5/6*(3/20+9/20)
=2/6*(12/20)]
=1/3 * 3/5
=1/5

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