a) 0,5=5/10=1/2
2,1=21/10
3,41=341/100
5,231=5231/1000
28,28=2828/100=707/25
9,501=9501/1000
8,678/1000=8678/1000=4339/250
101,53=10153/100
b)2,3=23/10
1,02=102/100=51/50
3,25=325/100= 65/20=13/4
12,4=124/10=31/5
20,15=2015/100=403/25
0,02=2/100=1/50
0,002=2/1000=1/500
0,0005=10000 =5/10000 =1/2000
0,625=625/1000=125/200=25/40=5/8