Question 1102021: In the arithmetic sequence given below, what term is the number negative 15?
5,10 thirds, 5 thirds,...
I am stuck after getting the difference which is the second term subtracted by the first term, which is negative 5 thirds. I know the formula for getting the answer for the missing term that being an=a1+(n-1). So I tried figuring out this one on my own, but end up with weird numbers, which is typical of doing arithmetic sequences that involve fractions. Also by the way the first term is 5 and the second term is 10 thirds.
Found 2 solutions by josgarithmetic, greenestamps:
Answer by josgarithmetic(39618)   (Show Source):
Answer by greenestamps(13200)  (Show Source):
You can put this solution on YOUR website!
If the fractions always seem to throw you off, then you can multiply every term in the sequence by 3 to make them whole numbers. Since you are only looking for which term in the sequence is -15, you will still get the right answer by doing this.
So now the sequence is
15, 10, 5, ...
and you are looking for which term is -45.
The common difference is now -5; and, as you showed in your statement of the problem,
an = a1 + (n-1)d
Solve this for n, knowing an is -45, a1 is 15, and d is -5:
The number -45 is the 13th term in the sequence.
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