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Bunuel
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IMO
If that sequence has n terms, it would be like this: 1,3,5,...,2n-1.
Its sum is (n/2)*(2n-1+1)=n^2=289 => n=17 representing the number of terms the sequence has.

rito54
Hello, how do we know it would be a perfect square? How do we get 17 terms? Is this really a 555-605 questions it seems a bit hard. thanks

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Difference in sequences: 1, 3, 5 (first consecutive odd numbers)
so their sum is n^2= 289 , n=17

now original sequence:
sum= avg*n=510, avg=30, middle term is 30 and sum of first 2 terms=avg*2=60.
final answer- 30+60=90
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