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What is the sum of the first hundred odd numbers?

Mathematics

ScanSolve AI Answer

Answer

D

Step-by-step solution

4 steps
  1. Identify the sequence of numbers.

    The first hundred odd numbers form an arithmetic progression: 1,3,5,…1, 3, 5, \dots.

  2. Determine the number of terms and the first term.

    We need the sum of the first hundred odd numbers, so the number of terms n=100n = 100.
    The first term a1=1a_1 = 1.

  3. Determine the last term.

    The nn-th odd number is given by the formula 2n−12n - 1.
    For the 100th odd number, a100=2(100)−1=200−1=199a_{100} = 2(100) - 1 = 200 - 1 = 199.

  4. Calculate the sum of the arithmetic progression.

    The sum of an arithmetic progression is given by the formula Sn=n2(a1+an)S_n = \frac{n}{2}(a_1 + a_n).
    Substitute the values:

    S100=1002(1+199)S_{100} = \frac{100}{2}(1 + 199) S100=50(200)S_{100} = 50(200) S100=10000S_{100} = 10000

    Alternatively, the sum of the first nn odd numbers is n2n^2.
    For n=100n=100:

    S100=1002S_{100} = 100^2 S100=100×100S_{100} = 100 \times 100 S100=10000S_{100} = 10000

    The sum of the first hundred odd numbers is 10000.

    Comparing this with the given options:
    A 200
    B 500
    C 1 000
    D 10 000
    E 100 000

    The correct option is D.

    The final answer is 10 000\boxed{\text{10 000}}.

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