五年级分数小数递等式计算题

23.5+14.8+36.5
=23.5+36.5+14.8
=60+14.8
=74.8
19.4+30.6+45.62
=50+45.62
=95.62
33.5+24.9+51.3
=58.4+51.3
=109.7
39.7×2.8+3.97×72
=3.97×10×2.8+3.97×72
=3.97×28+3.97×72
=3.97×（28+72）
=3.97×100
=397
32×1.2×52
=38.4×52
=1996.8
1.2×2+2.8×2
=【1.2+2.8】×2
=4×2
=8
2.5×2-1.5×2
=[2.5-1.5]×2
=1×2
=2
给我分啊 这7道题 费了我好大劲呢