What is a common ratio?
If you have a set of 3 or more numbers , such as 5 & 15
& 45 you will notice that 15 is 3 times the quantity as the
number preceding it. You also notice that 45 is 3 times as large as
the number preceding it . So we say that the RATIO between the
numbers is 3 in both cases. Hence there is a COMMON RATIO. The next
number in this series would need to also be in the ratio of 3 and
so the next number would be 45X3 equals 135.