a) 7/10 + 1/10 = (7+1)/10 = 8/10 = 4/5
б) 7/12 + 1/4 = 7/12 + (1*3)/(4*3) = 7/12 + 3/12 = (7+3)/12 = 10/12 = 5/6
в) 1/5 + 2/15 = (1*3)/(5*3) + 2/15 = 3/15 + 2/15 = (3+2)/15 = 5/15 = 1/3
г) 5/6 + 1/9 = (5*3)/(6*3) + (1*2)/(9*2) = 15/18 + 2/18 = (15+2)/18 = 17/18
д) 2/9 + 1/12 = (2*4)/(9*4) + (1*3)/(12*3) = 8/36 + 3/36 = (8+3)/36 = 11/36
е) 7/24 + 1/60 = (7*5)/(24*5) + (1*2)/(60*2) = 35/120 + 2/120 = (35+2)/120 = 37/120
ж) 1/42 + 2/63 = (1*3)/(42*3) + (2*2)/(63*2) = 3/126 + 4/126 = (3+4)/126 = 7/126 = 1/18
з) 5/12 + 3/20 = (5*5)/(12*5) + (3*3)/(20*3) = 25/60 + 9/60 = (25+9)/60 = 34/60 = 17/30