31.
2×3/4 = 6/4 = 1,5
6/5 ×10 = 60/5 = 12
5/8 × 16/35 = 80/280⁽¹⁰ = 8/28⁽⁴ = 2/7
10/3 × 0,3 = 3/3 = 1
20/9 × 9/5 = 180/45 = 4
