6.8x3.7+68x0.37=6.8x3.7+6.8x3.7=6.8x3.7x2=50.32
＝6.8×3.7＋6.8×3.7＝6.8×7.4＝（7－0.2）×（7＋0.4）＝49＋0.2×7－0.08＝50.32
