1) ( 17/150 ) + ( 13/150 ) = 30/150 = 1/5
2) ( 78/150 ) + ( 28/150 ) = 106/150 = 53/75
3) ( 52/270 ) + ( 38/270 ) = 90/270 = 1/3
4) ( 157/270 ) - ( 97/270 ) = 60/270 = 2/9
5) ( 123/350 ) - ( 53/350 ) = 70/350 = 1/5
6) ( 39/350 ) + ( 11/350 ) = 50/350 = 1/7
7) ( 107/420 ) + ( 103/420 ) = 210/420 = 1/2
8) ( 287/420 ) - ( 117/420 ) = 170/420 = 17/42