Выражение 1)3/4х×2/3; 2)1,6у×5; 3)5/6х×3/5; 4)0,8у×10; 5)2/9х×3/4; 6)1,25у×4.

1) 3/4х * 2/3 = (3/4 * 2/3)х = 1/2х
2) 1,6у * 5 = (1,6 * 5)у = 8у
3) 5/6х * 3/5 = (5/6 * 3/5)х = 1/2х
4) 0,8у * 10 = (0,8 * 10)у = 8у
5) 2/9х * 3/4 = (2/9 * 3/4)х = 1/6х
6) 1,25у * 4 = (1,25 * 4)у = 5у

Пояснения:
3/4 * 2/3 = (1*1)/(2*1) = 1/2
5/6 * 3/5 = (1*1)/(2*1) = 1/2
2/9 * 3/4 = (1*1)/(3*2) = 1/6