1.10*18.6=(1+0.1)*18.6=1*18.6+0.1*18.6=18.6+1.86=20.46
9.99*2.5=(10-0.01)*2.5=10*2.5-0.01*2.5=25-0.025=24.975
68/25=(68*4)/(25*4)=272/100=2.72
3.4*1.2-0.65 =3.4*1+3.4*0.2-0.65=3.4+0.68-0.65=3.4+0.03=3.43