https://prepswift.gregmat.com/quizzes/quiz/prepswift-series-i (Question 7)
Is it wrong to solve the question this way:
7260 < (x-3+1)/4 * (3+x)/2*
–>* 7260*8 < (x-2)(3+x)
–> 0 < x^2 + x - 58,086
Plug in values from the given options –> anything when x^2 + x is greater than 58,086 is a valid solution.
This yields the same answer but is a different avenue than the solution.
No.
Your approach is correct but your work has a a small mistake so you may have gotten lucky.
You are essentially using the Sum of an Arithmetic Sequence formula.
First term = 3
Last term = n but you used x.
Number of terms (where you made the mistake) =
=Mean/Median =
Sum = 
The correct inequality therefore must be,
I say you were lucky because the mistake you made while finding the number of terms - adding the 1 in the bracket, when it should be outside of the bracket- could have led you to wrong answers. In this particular case, it didn’t.
If this is the final inequality, why is 240 also not in the answer?
How to eliminate that?
240 is not/cannot be a term of the series.
Remember that n MUST be a term of the series.
239 and 243 are the terms before and after 240.
Got it. Thank you
