A child arranges marbles in rows so that the first row has 1 marble, the second has 2 marbles, the third has 3, and so on up to 25 rows. How many marbles does the child use in all?

Question

TextSum of First n Natural Numbers

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Find all possible ways of expressing 100 as the sum of consecutive natural numbers.

Find the smallest value of n such that the sum of the first n natural numbers is greater than 1,000.

Find the 20th term of the series 2 × 4 + 4 × 6 + 6 × 8 + ... + n terms.

Find the sum of :