Skip to main contentSkip to solution

Find the sum of the first n positive integers.

Solution

✅ Correct Option: 3

Pairing the first and last terms of 1+2+⋯+n1 + 2 + \dots + n gives n/2n/2 pairs each summing to (n+1)(n+1), so the total is n(n+1)2\dfrac{n(n+1)}{2}. Checking n=3n = 3: 1+2+3=6=3×421+2+3 = 6 = \dfrac{3 \times 4}{2}.

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question