简便运算题1/7+2/7+3/7+4/7+.+18/7+19/7+20/7 100/(100/99)/(99/98)./(4/3)/(3/2)/(2/1)

1/7+2/7+3/7+4/7+.+18/7+19/7+20/7
=1/7×（1+2+3+4+……+18+19+20）
=1/7×（1+20）×20÷2
=1/7×21×10
=30
100/(100/99)/(99/98)./(4/3)/(3/2)/(2/1)
=100×99/100×98/99×……×3/4×2/3×1/2
=1