28 000 :70 = (28*1000) /(7*10)=4*100=400
7 800 :30 = (78*100)/(3*10)=(3*26*100) /(3*10)=26*100=2600
4 800 :20 = (48*100)/(2*10)=(2*24*100) /(2*10)=24*100=2400
36 000 :600 = (36*1000)/(6*100)=(6*6*1000) /(6*100)=6*10=60
4 900 :700 = (49*100)/(7*100)=(7*7*100) /(7*100)=7
3 200 :400 = (32*00)/(4*100)=(4*8*100) /(4*100)=8
600:12=(60*10)/12=(5*12*10)/12=5*10=50
650:25=(65*10)/(5*5)=(5*13*5*2)/(5*5)=2*13=26
840:21=(84*10)/21=(21*4*10)/21=4*10=40