5.6×3.5
=0.7×8×0.7×5
=(0.7×0.7)×（8×5）
=0.49×40
=4.9×4
=19.6
5.6×3.5
=7×0.8×0.7×5
=（7×0.7）×（0.8×5）
=4.9×4
=（5-0.1）×4
=5×4-0.1×4
=20-0.4
=19.6
5.6×3.5
=0.7×8×0.7×5
=(0.7×0.7)×（8×5）
=0.49×40
=4.9×4
=19.6
5.6×3.5
=7×0.8×0.7×5
=（7×0.7）×（0.8×5）
=4.9×4
=（5-0.1）×4
=5×4-0.1×4
=20-0.4
=19.6