计算：（1）299.9×19.98-199.8×29.97；（2）3.14+64.8×0.537×25+5.37×6.48×75-8×64.8×0.125×53.7；（3）27.8×28.7-27.7×28.8；（4）24.25×7.19+0.23×281+1.25×0.81；（5）0.1+0.3+0.5+0.7+0.9+0.11+0.13+0.15+0.17+0.19+0.21+…+0.99

Question

计算：
（1）299.9×19.98-199.8×29.97；
（2）3.14+64.8×0.537×25+5.37×6.48×75-8×64.8×0.125×53.7；
（3）27.8×28.7-27.7×28.8；
（4）24.25×7.19+0.23×281+1.25×0.81；
（5）0.1+0.3+0.5+0.7+0.9+0.11+0.13+0.15+0.17+0.19+0.21+…+0.99；
（6）999999×222222+333333×333334；
（7）1981×198319831983-1982×198119811981．

Answer 1

（1）299.9×19.98-199.8×29.97
=29.99×199.8-199.8×29.97
=（29.99-29.97）×199.8
=0.02×（200-0.2）
=0.02×200-0.02×0.2
=4-0.004
=3.996；

（2）3.14+64.8×0.537×25+5.37×6.48×75-8×64.8×0.125×53.7
=3.14+6.48×5.37×25+5.37×6.48×75-8×12.5×5.37×6.48
=3.14+（25+75）×6.48×5.37-100×6.48×5.37
=3.14+100×6.48×5.37-100×6.48×5.37
=3.14+（100-100）×6.48×5.37
=3.14+0×6.48×5.37
=3.14+0
=3.14；

（3）27.8×28.7-27.7×28.8
=27.8×（28.8-0.1）-（27.8-0.1）×28.8
=27.8×28.8-27.8×0.1-27.8×28.8+28.8×0.1
=（27.8×28.8-27.8×28.8）-2.78+2.88
=0+2.88-2.78
=0.1；

（4）24.25×7.19+0.23×281+1.25×0.81
=（23+1.25）×7.19+23×2.81+1.25×0.81
=23×7.19+1.25×7.19×23×2.81+1.25×0.81
=（7.19+2.81）×23+（7.19+0.81）×1.25
=10×23+8×1.25
=230+10
=240；

（5）0.1+0.3+0.5+0.7+0.9+0.11+0.13+0.15+0.17+0.19+0.21+…+0.99
=（0.1+0.9）×5÷2+（0.11+0.99）×45÷2
=2.5+24.75
=27.25

（6）999999×222222+333333×333334
=333333×（3×222222）+333333×333334
=333333×666666+333333×333334
=（666666+333334）×333333
=1000000×333333
=333333000000；

（7）1981×198319831983-1982×198119811981
=1981×1983×1000100010001-1982×1981×1000100010001
=（1983-1982）×1981×1000100010001
=198119811981．