CA Foundation · Quantitative Aptitude · Sequence and Series
What is the value of 1³ + 2³ + 3³ + ... + 15³?
The sum is 14400. The sum of the cubes of the first n natural numbers equals the square of their sum. For n = 15 the sum of the numbers is 120, and 120 squared is 14400.
- A14400Correct
- B13600
- C120
- D12100
Explanation
Sum of cubes = [n(n+1)/2]². For n = 15, n(n+1)/2 = 120, and 120² = 14400. The value 120 is only the sum of the first 15 natural numbers, and it must be squared.
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