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find the number of terns of an arithmetic series such that the sum is 10, c
ommon difference is 9 and the last term is 20

a. 8 b. 7 c. 6 d. 5​


Sagot :

ARITHMETIC SERIES

Find the number of terms of an arithmetic series such that the sum is 10, common difference is 9 and the last term is 20.

a. 8 b. 7 c. 6 d. 5

SOLUTION:

  • Given the last term and the common difference, this is easy.
  • Just simply subtract the common difference from the last term, so on and so forth.

20 - given term

[tex]20 - 9 = 11[/tex]

[tex]11 - 9 = 2[/tex]

[tex]2 - 9 = -7[/tex]

[tex]-7 - 9 = -16[/tex]

  • There are 5 terms.
  • To check, add the following terms, the answer should be 10.

[tex]20 + 11 = 31[/tex]

[tex]31 + 2 = 33[/tex]

[tex]33 + (-7) = 26[/tex]

[tex]26 + (-16) = 10[/tex] ✔︎

ANSWER:

The answer is 5. Letter D.

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