30) A) 5/3-5/6*7/10=5/3-(5*7)/(6*2*5)=5/3-7/12=20/12-7/12=13/12
B) 2/5-1/5*4/3=2/5-(1*4)/(5*3)=2/5-4/15=6/15-4/15=2/15
31) A) 5/4*1/3-5/6*1/2=(5*1)/(4*3)-(5*1)/(6*2)=5/12-5/12=0
b) 5/4*(1/3-5/6)*1/2=5/4*(2/6-5/6)*1/2=5/4*(-3/6)*1/2=-(5*3*1)/(4*2*3*2)=-5/16