Ask questions and get helpful answers.

Find the exact value (either decimal or fractional form) of the first term of an arithmetic sequence if the sum of the first 100 terms is 7099.5 and the sum of the next 100 terms is 20799.

  1. 👍
  2. 👎
  3. 👁
  4. ℹ️
  5. 🚩

2 answers

  1. We find a from a system:
    a +a+99d =7099.5
    a+100d+a+199d=20799

    We subtract from the 2nd the 1st:

    200d=13699.5
    d=68.4975

    2a+99x68.4975=7099.5
    a=159.12375 (0.12375=99/800)

    1. 👍
    2. 👎
    3. ℹ️
    4. 🚩
  2. Ummm.

    Sn = n(a1 + an)/2
    S100 = 100(a1 + a100)/2
    = 50(a+a+99d)
    = 100a + 4950

    1. 👍
    2. 👎
    3. ℹ️
    4. 🚩

Answer this Question

Related Questions

Still need help?

You can ask a new question or browse existing questions.