For the first ratio:

3:4.5 = 2 1/2:3 3/4

To simplify both sides of the ratio, we can convert 4.5 to a mixed number, which is 4 1/2.

So, the ratio becomes:

3:4.5 = 2 1/2:4 1/2

To express both sides of the ratio as improper fractions:

3:4.5 = 6/2:9/2

Now, we can simplify the ratio:

6/2 ÷ 2 = 3
9/2 ÷ 2 = 9/4

So, the simplified ratio is:

3:9/4 or 3:2 1/4

For the second ratio:

5:2.5 = 20:16

To simplify, we can convert 2.5 to a whole number by multiplying both sides by 2:

52:2.52 = 10:5

Now, we simplify this ratio:

10:5 = 20:10

Dividing both sides by 10, we get:

20/10 ÷ 10 = 2/1

So, the simplified ratio is:

20:16