unknown base system: how can they say base is more than 6?

[defeated_soldier]

a number is written in a unknown base system . the number is 3326.

My book says , Since 6 is the highest number used , the base has to be more than 6

I dont understand it . how the book can conclude this ? is this valid ? however , does the book only picking up the units digit or any bigger didgit in the number needs to picked up for a judgement ?

if the numberr was 7623 , then can we say base >7 ? // is this true
if the numberr was 7693 , then can we say base >9 ? // is this true

 

[Denis]

Yes; all true.

Good explanation here:
http://mathforum.org/library/drmath/view/55739.html