The sum of the first n even natural numbers is 1560. Find the value of n.
A41
B39 ✓ Correct
C40
D38
Correct answer: (B) 39
Explanation
n = 39.
Sum of first n even numbers = n(n + 1).
n(n + 1) = 1560.
n^2 + n - 1560 = 0, n = (-1 + sqrt(6241)) / 2.
sqrt(6241) = 79, so n = 78 / 2 = 39.
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