Номер 20
1)2/5+1,83=0,4+1,83=2,23
2)6,4-3/20=6,4-0,15=6,25
3)9,8*3/10=9,8*0,3=2,94
4)7,2:1/100=7,2:0,01=720
Номер 21
1)8,5-1/3=8_5/10-1/3=8_5/10-1/3=8_5/10-1/3=255-10/30=245/30=49/6=8_1/6
2)4_1/9+1,8=4_1/9+1_9/10=(4+1)+(1/9+8/10)=5+_10+72/90=5+_82/90=5+_41/45=5_41/45
3)1/9*0,12=1/9*12/100=1/3*1/25=1/75
4)6/7:0,6=6/7:6/10=6/7*10/6=10/7=1_3/7