计算 9999×7778+3333×6666 1/20+1/30+1/42+1/5
问题描述：
计算 9999×7778+3333×6666 1/20+1/30+1/42+1/5
答
9999×7778+3333×6666
=9999×7778+9999×2222
=9999×（7778+2222）
=9999×10000
=99990000
1/20+1/30+1/42+1/56+1/72+1/90
=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1/4-1/10
=3/20