math

posted by Brittany

The third and seventh terms of an arithmetic sequence are 10 and 20.
1) What is the value of the 1st term?
2) What is the value of the 9th term?
3) What is the equation to find the nth term in the sequence?

HELP!! PLEASE!!

  1. helper

    Arithmetic sequence
    a, a + d, a + 2d, a + 3d, ...a +(n - 1)d

    1)a3 = 10, a7 = 20
    Since these are 4 places apart (7 - 3 = 4)

    a7 = a3 + 4d
    20 = 10 + 4d
    10 = 4d
    d = 10/4 = 2.5
    So, the common difference, d = 2.5

    To find the 1st term a,
    a3 = a + 2d
    10 = a + 2(2.5)
    10 = a + 5
    a = 5

    2) to find 9th term
    a9 = a + 8d
    a9 = 5 + 8(2.5)
    a9 = 5 + 20
    a9 = 25

    3) nth term
    Last term = a + (n - 1)d
    an = 5 + (n - 1)(2.5)

  2. switee

    4a2

Respond to this Question

First Name

Your Answer

Similar Questions

  1. Mathematics : Arithmetic Sequence

    The 5th term and the 8th term of an arithmetic sequence are 18 and 27 respctively. a)Find the 1st term and the common difference of the arithmetic sequence. b)Find the general term of the arithmetic sequence.
  2. 9th grade math honors

    suppose t(1)=-91 and -67 is another term of an arithmetic sequence, with. What is the equation of the nth term of the sequence if there are n terms between these two?
  3. Arithmetic Sequence

    Given the third term of an arithmetic sequence less than the fourth term by three. The seventh term is two times the fifth term. Find the common difference and the first term.
  4. Math *URGENT

    Please give the answers and solutions for each. 1.If the second term is 2 and the seventh term of a geometric sequence is 64, find the 12th term. 2. Which term if the geometric sequence 18,54,162,486,... is 3,188,646?
  5. Math

    1. Find the 12th term of the arithmetic sequence 2, 6, 10, … . 2. Solve for the 101st term of the sequence whose 1st term is x-y and d=2x+y-3. 3. In the sequence 2, 6, 10, … , what term has a value of 106?
  6. arithmetic

    Determining the first three terms of an ArithmetiC progressionof which the (a.)10th term is 31 and the 15th term is 49 (b.)7th term is 3 and 12th term is -3 (c.)5th term is 8 and the 11th term is -28 (d.)9th term is7+9x and d=2x,Show …
  7. Math

    Find the 10th term of a nonconstant arithmetic sequence whose 1st term is 3 with the 1st, 4th, and 13th term forming a geometric sequence. I've tried doing it differently everytime, but I always come to a dead end..
  8. math

    The 1st,5th,13th term of an arithmetic sequence are the first 3 terms of geometric sequence with a common ratio of 2. If the 21st term of the arithmetic sequence is 72, calculate the sum of the first 10 terms of the geometric sequence.
  9. math

    in an arithmetic sequence 17th term is 9 times the first three terms and the 9th term is 6 less than 3 times the 1st term. Find the first three terms
  10. Math

    The fourth term of an arithmetic sequence is less than the fifth term by 3. The seventh term is three times the fifth term. Find the common difference and the first term

More Similar Questions