1) 3 : 1/7 = 3 * 7 = 21
2) 2/9 * 3/4 = 2*3/9*4 = 1*1/3*2 = 1/6
3) 4*1/5 +5*2/15 = 21/5 * 77/15 = 21*77/5*15 = 7*77/5*3 = 539/15
4) 4/35 : 8/14 = 4/35 * 14/8 = 4*14/35*8 = 1*2/5*2 = 2/10
5) 1/2 - 1/5 = 5*(1/2) - 2(1/5) = 5/10 - 2/10 = 3/10
6) 1,7 : 10/17 = 17/10 : 10/17 = 17/10 * 17/10 = 289/100 = 2,89
7) 1*1/2 : 4/27 = 3/2 : 4/27 = 3/2 * 27/4 = 3*27/2*4 = 81/8