If the sum of the first n natural numbers is 55, what is n?

Practice Questions

Q1
If the sum of the first n natural numbers is 55, what is n?
  1. 10
  2. 11
  3. 12
  4. 9

Questions & Step-by-Step Solutions

If the sum of the first n natural numbers is 55, what is n?
  • Step 1: Understand that the sum of the first n natural numbers can be calculated using the formula n(n + 1)/2.
  • Step 2: Set the formula equal to 55, since we know the sum is 55. This gives us the equation n(n + 1)/2 = 55.
  • Step 3: To eliminate the fraction, multiply both sides of the equation by 2. This gives us n(n + 1) = 110.
  • Step 4: Now, we need to solve the equation n(n + 1) = 110. This means we need to find two consecutive numbers that multiply to 110.
  • Step 5: Start testing natural numbers for n. If n = 10, then n + 1 = 11. Check if 10 * 11 = 110. It does, so n = 10 is correct.
  • Step 6: Conclude that the value of n is 10.
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