Đáp án+Giải thích các bước giải:
`1.39`
`d) 19.8=19.2.2.2=38.2.2=76.2=152`
`1.40`
`a) 91.11=(100-9).11=11.100-11.9=1100-99=1001`
`b) 45.12=(40+5).12=40.12+5.12=480+60=540`
`1.42`
`a) 5.11.18+9.31.10+4.29.45`
`=5.18.11+9.10.31+2.2.29.45`
`=(5.18).11+(9.10).31+(2.45).29.2`
`=90.11+90.31+90.58`
`=90.(11+31+58)`
`=90.100`
`=9000`
`b) 37.39+78.14+13.85+52.55`
`=37.39+39.2.14+13.5.17+13.4.11.5`
`= 37.39+39.28+65.17+65.44`
`= 39.(37+28)+65.(17+44)`
`= 39.65+65.61`
`=65.(39+61)`
`=65.100`
`=6500`
