Đáp án:
`a,-1+45/115+47/51+ -9/23+ -1/3`
`=-1+9/23+47/51+ -9/23+ -1/3`
`=(-1+47/51-1/3)+(9/23 + -9/23)`
`=-7/17`
`b,-13/49+12/48+1/12+3/18`
`=-13/49+1/4+1/12+3/18`
`=-13/49+(1/4+1/12+3/18)`
`=-13/49+1/2=23/98`
`c,13/15+(-4/5 +7/18)+ - 5/12+1/36`
`=13/15-4/5+7/18-5/12+1/36`
`=(13/15-4/5)+(7/18-5/12+1/36)`
`=1/15`