Two quantities
can be compared in a variety of ways. For example, if two brothers
David and John weigh 50 kg and 75kg respectively, then John could
be described as 25 kg heavier than David, or 1 1/2 times as
heavy as his brother. Alternatively, their weights could be given
as being in the ratio of 50 : 75, which simplifies on division by
25 to the ratio 2 : 3

If a class of students
has 12 boys and 16 girls then the ratio of boys to girls is 12:16,
which simplifies to 3:4 on division by 4.

In general the value of a ratio is unchanged when the numbers forming
it are both multiplied (or divided) by a constant. so for example,
24 : 40 = 12 : 20 = 6 : 10 = 3 : 5 = 9 : 15 = 45 : 75