4.67 would be a rounded answer. Really it's 4.666666666666666666 (the 6 go on forever) but we can't write that out.
Answer: Third option.
Step-by-step explanation:
You know that the drawbridge rises at a rate of 
feet per minute. This means that the drawbridge rises in a minutes.
Convert from mixed fraction to decimal number:
Since the drawbridge rises to a height of 50 feet, you need to apply this procedure in order to find the time the drawbridge takes to completely rise:
or 
The 1st term is 60.
Add 50 to this to get the 2nd term, 60 + 50 = 110.
Add 50 to that to get the 3rd term, 110 + 50 = 160.
Add 50 to that to get the 4th term, 160 + 50 = 210.
And so on...
Notice that in the 2nd term, we added 1 copy of 50 to the 1st term.
In the 3rd, we ultimately added 2 copies of 50 to the 1st term.
In the 4th, we added 3 50s.
And so on... If the pattern continues, then the <em>n</em>-th term can be obtained by adding (<em>n</em> - 1) copies of 50 to the first term.
So, the 100th term is
60 + (100 - 1) * 50 = 5010
