помогите решить: 3/25*5/6*10/9=?, 8*9/16-*7/12=?, 3/8*2/15:7/20=?, 4/9:8/9*10/17=?

1) 3/25 * 5/6 * 10/9 = (3*5*2*5)/(5*5*2*3*9) = 1/9

2) 8 * 9/16 * 7/12 = (8*3*3*7)/(2*8*3*4) = 21/8

3) 3/8 * 2/15 : 7/20 = (3*2*20)/(8*15*7) = 1/7

4) 4/9 : 8/9 * 10/17 = (4*9*10)/(9*8*17) = 5/17