(33/17+20/13+33/7)/(3/7+3/13+3/17)
=(33/17+33/13+33/7-13/13)/(3/7+3/13+3/17)
=(33/17+33/13+33/7-1)/(3/7+3/13+3/17)
=(33/17+33/13+33/7)/(3/7+3/13+3/17)-1/(3/7+3/13+3/17)
=11*(3/17+3/13+3/7)/(3/7+3/13+3/17)-1/(3/7+3/13+3/17)
=11-1/(3/7+3/13+3/17)
=11-1/(3*(1/7+1/13+1/17))
=11-1/(3*((221+119+91)/1547))
=11-1/(3*(431/1547))
=11-1/(1293/1547)
=11-1547/1293
=11-1又(254/1293)
=9又(1039/1293)