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1) 1/5 + 17/20 = 4/20 + 17/20 = 21/20 = 1 1/20 2) 1/7 - 1/14 = 2/14 - 1/14 = 1/14 3) 3/10 + 3/4 = 6/20 + 15/20 = 21/20 = 1 1/20 4) 28/57 - 3/19  =28/57 - 9/57 = 19/57 = 1/3 5) 2/25 + 0,02 = 2/25 + 2/100 = 8/100 + 2/100 = 10/100 = 1/10 = 0,1 6) 2 1/8 - 1 1/4 = 17/8 - 5/4 = 17/8 - 10/8 = 7/8 7) 1 3/5 + 0,5 = 8/5 + 5/10 = 16/10 + 5/10 = 21/10 = 2 1/10 = 2,1 8) 5 1/7 - 3 1/14 = 5 2/14 - 3 1/14 = 2 1/14 9) 4 - 3 4/9 = 3 9/9 - 3 4/9 = 5/9 10) 3 7/15 + 1 8/15 = 4 15/15 = 5 11) 2 7/16 + 1 9/16 = 3 16/16 = 4 12) 1 1/2 - 1/4 = 1 2/4 - 1/4 = 1 1/4 13) 2 2/5 + 1,5 = 12/5 + 15/10 = 24/10 + 15/10 = 39/10 = 3 9/10 14) 4 1/6 - 2 1/18 = 4 3/18 - 2 1/18 = 2 2/18 = 2 1/9 15) 1 5/8 + 2 7/8 = 3 12/8 = 3 4/3 = 4 1/3