(7/15-1/6)+2/5=(14/30-5/30)+2/5=9/30+12/30=21/30=7/10
(3/8-1/9)+25/36=(27/72-8/72)+25/36=19/72+50/72=69/72=23/24
(8/9-5/6)+2/3=(16/18-15/18)+2/3=1/18+12/18=13/18
(7/8-13/20)+9/10=(35/40-26/40)+9/10=9/40+36/40=45/40=1 и 1/8
(7/18-1/12)+5/6=(14/36-3/36)+5/6=11/36+30/36=41/36=1 5/36
(3/4-8/15)+17/20=(45/60-32/60)+17/20=13/60+51/60=64/60=1 и 1/15