I was taking a practice GMAT test and it had a question like this:
$4^{21} \cdot 5^{11} = 2 \cdot 10^n$
What is $n$?
The available answers were something like
16
22
23
24
32
I'm not exactly sure on the multiple choice options...
However I'm not allowed a calculator so I'm not sure how to go about this...
I'm generally pretty good at the little tricks that allow you to solve a questions without the calculator but I have no idea how to do this one...
Thanks!
Update:
I found the actual question: