what is 19/27+5/18+(-1/10)?

Get a common denominator:

     27  =  3x3x3

     18  =  2x3x3

     10  =  2x5

Lowest common denominator:  2x3x3x3x5  =  270

19/27:    since 27 goes into 270 10 times, multiply by 10/10  to get  190/270

5/18:      since 18 goes into 270 15 times, multiply by 15/15 to get 75/270

1/10:      since 10 goes into 270 27 times, multipoly by 27/27 to get 27/270

19/27 + 5/18 + (-1/10)    becomes    190/270 + 75/270 + (-27/270)    =    238/270    =  119/135