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.
#CarryOnLearning
