(4/5-7/20)/[1/4-20%(1+25%)+2%]
=(16/20-7/20)/[1/4-(1/5)*(5/4)+2%]
=(9/20)/(1/4-1/4+1/50)
=(9/20)/(1/50)
=(9/20)*50
=45/2
脱式计算：（五分之四减二十分之七）除[四分之一减20%(1+25%)+2%] （求计算过程）
(4/5-7/20)/[1/4-20%(1+25%)+2%]
=(16/20-7/20)/[1/4-(1/5)*(5/4)+2%]
=(9/20)/(1/4-1/4+1/50)
=(9/20)/(1/50)
=(9/20)*50
=45/2