1)2,0125+2 3/16=2 125/10000 + 2 3/16 = 4 + 125/10000 + 3/16 = 4 + 125·1/10000·1 + 3·625 16·625 = 4 + 125/10000 + 1875/10000 = 4 + 125 + 1875/10000 = 4 2000/10000 = 4 1·2000/5·2000 = 4 1/5
2)2/3-1/5= 2·5/3·5 - 1·3/5·3 = 10/15 - 3/15 = 10 - 3/15 = 7/15
3)4 1/5: 7/15=21/5•15/7=21·15/5·7 = 315/35 = 9·35/35= 9