What is the difference between part to part ratio and a part to whole ratio ?

Ratios can be part-to-part, part-to-whole, or whole-to-part. Let's take a look at what this means.

When we compare boys to girls in a classroom, we are comparing part of the class to another part of the class. This would be a part-to-part comparison.

When we compare boys to the whole class, this is a part-to-whole comparison.

If we were to compare the class to the girls, this would be whole-to-part comparison.

EXAMPLE: A class is made up of 14 girls and 15 boys. 

PART_TO_PART 14 : 15 shows girls to boys

PART_TO_WHOLE 14: 29 shows girls to the class

Whole-to-Part 29 : 14 shows the class to the girls

19. C. 10,12 (D is eliminated because 15 is greater than 12, greatest common factor of the others was not 2)

20. C. 42 (The largest integer that can divide into both)