# What is the common ratio in this geometric sequence 3, 18, 108, 648, 3888, ...?

Nov 9, 2015

The ratio is $6$.

#### Explanation:

A term in a geometric series are obtained by multiplying the previous one by a fixed value, called ratio, which we will call $r$.

So, the second term $18$ is obtained by the first, $3$, multiplying by a value which we can easily find: if $18 = 3 \cdot r$, then $r = \frac{18}{3} = 6$.

The same goes for the third, since $108 = 18 \cdot 6$, and so on.

You can check that also the reimaining terms obey this rule, so the ratio is $6$.