a= 10sur21 - 1sur42 + 5sur2
a=20sur42 - 1sur42 + 30sur42
a=49sur42
a=7sur6
b=1sur3 + 1sur6 +1sur9 + 1sur 18
b=6sur18+3sur18+ 2sur18 +1sur18
b=12sur 18
b=2 sur 3
c= 17sur 40 +3sur10 - 3sur5
c=17sur40+ 12sur40- 24sur 40
c=53sur 40
d=1sur4 - 1sur 7 +1sur14-1sur28
d=7sur28-4sur28+2sur28-1sur28
d=4sur28
d=1sur7
