3:4.5=2 1/2:3 3/4 5:2.5=20:16

1.

3 : 4,5 = 3 : 4 5/10 = 3 : 45/10 = 3 × 10/45 = (3 × 10)/45 = 30/45 = 6/9 = 2/3;

Ответ: 3 : 4,5 = 2/3.

2.

2 1/2 : 3 3/4 = (2 × 2 + 1)/2 : (3 × 4 + 3)/4 = 5/2 : 15/4 = 5/2 × 4/15 = (5 × 4)/(2 × 15) = (1 × 2)/(1 × 3) = 2/3.

Ответ: 2 1/2 : 3 3/4 = 2/3.

3.

5 : 2,5 = 5/1 : 2 5/10 = 5/1 : (2 × 10 + 5)/10 = 5/1 : 25/10 = 5/1 × 10/25 = (5 × 10)/(1 × 25) = (1 × 10)/(1 × 5) = 10/5 = 2/1 = 2.

Ответ: 5 : 2,5 = 2.

4.

20 : 16 = 20/16 = (5 х 4)/(4 х 4) = (5 х 1)/(4 х 1) = 5/4 = 1 1/4 = 1 25/100 = 1,25.

Ответ: 20 : 16 = 1 1/4 = 1,25.