20-19+18-17.........+4-3+2-1
=(20-19)+(18-17)+......+(4-3)+(2-1)
=1+1+1+......+1(10个销配迟亏李卖御1)
=10
10*1=10
20-19+18-17.........+4-3+2-1用简便方法计算
20-19+18-17.........+4-3+2-1
=(20-19)+(18-17)+......+(4-3)+(2-1)
=1+1+1+......+1(10个销配迟亏李卖御1)
=10
10*1=10
20-19+18-17.........+4-3+2-1
=(20-19)+(18-17)+......+(4-3)+(2-1)
=1+1+1+......+1(10个销配迟亏李卖御1)
=10
10*1=10