Question 1207776
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Answer: <font color=red>1,099,511,627,776</font>
This is roughly 1.0995 trillion


Work Shown
4^20 = 1099511627776


Explanation
Let's say for the sake of simplicity there are 2 questions with 4 options each.
Consider a 4 by 4 table. There are 4*4 = 4^2 = 16 different ways to answer these two questions. 
This is because there are 16 inner cells of this table.


Now consider a test with 3 questions. Each has 4 options.
We found earlier that there are 16 ways to answer the first two questions. 
Consider a table that has 16 rows and 4 columns. 
The row count is how many ways to answer the first two questions, while the columns are the options for the third question.
We have 16*4 = 64 ways to answer these 3 questions
Or put another way 4^3 = 64
This pattern can be continued for as long as you like.


In general, if an exam has n questions with 4 options each, then there will be 4^n different ways to select the options.
In the "work shown" section above, I plugged in the value n = 20. 
The massive number 1099511627776 is roughly 1.0995 trillion.
In scientific notation, it's roughly equal to 1.0995 * 10^12
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