[latexpage]

# Algebra

Given 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 Sn be the sum of the elements in the nth set. Find S15.

### See our previous ‘Questions of the Day’:

1. In n the set there are n elements so in the 15th set there are 15 elements.

and the last element of nth set is (1 + 2 + 3 + 4 +…. n)th positive integer

Hence ,the last element of S15 = 15 x 16/2 = 120.

• Nice instruction, thanks

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