# How do you find the common ratio for 7,14,28,56,128,...?

Jul 24, 2016

Ignoring the $128$ (which should probably have been $112$), the common ratio is $2$.

#### Explanation:

For this sequence to have a common ratio, the ratio between any pair of consecutive terms must be the same.

So if this sequence does have a common ratio, then we can look at any pair of consecutive terms, e.g. $7 , 14$ to find the ratio:

$\frac{14}{7} = 2$

This ratio is the same for $\frac{28}{14}$ and $\frac{56}{28}$, but $128 \ne 2 \cdot 56$.

I suspect a typo in the question. The value you would expect is $112$ rather than $128$.