The ratio of a number a to a number b can be represented as a fraction a/b, which is the same as a:b.
To find the requested ratios, first find the amount of circles of each color on the picture:
Red circles: 4
Yellow circles: 3
Blue circles: 3
Green circles: 5
Total number of circles: 15
3)
To find the ratio of red circles to yellow circles, use the number of red circles (4) as numerator and the number of yellow circles (3) as denominator:

Since this fraction is already written in its lowest terms, the ratio of red circles to yellow circles is:

4)
Using a similar procedure, the ratio of blue circles to green circles is:

5)
First, write the ratio of yellow circles to blue circles as a fraction:

This fraction can be simplified since both numerator and denominator are multiples of 3:

Since the fraction 1/1 is equivalent to 3/3, then the ratio of yellow circles to blue circles is:

6)
First, write the ratio of blue circles to the total number of circles as a fraction and simplify it:

Then, the ratio of blue circles to the total number of circles is:

7)
First, write the ratio of green circles to the total number of circles as a fraction and simplify it:

Then, the ratio of green circles to the total number of circles, is:
