Bunuel
Consider the sets of consecutive integers {1}, {2, 3}, {4, 5, 6}, {7, 8, 9, 10}, ..., where each set contains one more element than the preceding one, and where the first element of each set is one more than the last element of the preceding set. Let \(S_n\) be the sum of the elements in the \(n_{th}\) set. What is the value of \(S_{50}\)?
(A) 42,455
(B) 61,250
(C) 62,525
(D) 65,525
(E) None of these
So \(1^{st}\) set has 1 element, while the \(2^{nd}\) has 2 elements and so on.
Thus the \(50^{th}\) set will have 50 elements.
Let us check on the largest digit in each set now.
\(1^{st}\) set has 1, while the \(2^{nd}\) has 3 and \(3^{rd}\) has 6 and so on.
What is the connection between (1 and 1); (2 and 3) and (3 and 6).
The second digit is the SUM of the positive integers till the first integer => (n and Sum of first n positive integers)
So, in the 50th set, it will be 'Sum of first n positive integers'=\(\frac{50*51}{2}=1275\) =>(50 and 1275)
So 50th set has 50 elements and the largest is 1275...{a,.....,1275} => a=1275-50+1=1226
{1226,1227,....1274,1275}
\(S_{50}=1226+1227+....1274+1275=\frac{1226+1275}{2}*50=62,525\)
C