21-3分之4-15分之4-35分之4-63分之4-99分之4-143分之4-195分之4
=21-4(1/3+1/15+1/35+1/63+1/99+1/143+1/195
=21-2(1/1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13+1/13-1/15)
=21-2(1-1/15)
=21-28/15
=21-1-13/15
=20-13/15
=19又15分之2
21-3分之4-15分之4-35分之4-63分之4-99分之4-143分之4-195分之4
=21-4(1/3+1/15+1/35+1/63+1/99+1/143+1/195
=21-2(1/1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13+1/13-1/15)
=21-2(1-1/15)
=21-28/15
=21-1-13/15
=20-13/15
=19又15分之2