In the arithmetic sequence t1, t2, t3....tn t1 = 23 and tn=tn-1 - 3 for each n>1.
What is the value of n when tn = -4
A) -1
B) 7 *
C) 10
D) 14
E) 20
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- rfernandez
- Course Students
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- Joined: Fri Apr 07, 2006 8:25 am
One of many approaches:
We know that each term is 3 less than the previous term. We also know that the "distance" between the first term 23 and the term -4 is -4 - 23 = -27. So, that tells us that the term -4 is -27/-3 = 9 terms away from the first term. So the answer is 10.
Another approach is simply to list out the pertinent terms of the sequence:
23, 20, 17, 14, 11, 8, 5, 2, -1, -4. Here it's really clear that n is 10 when tn is -4.
Rey
We know that each term is 3 less than the previous term. We also know that the "distance" between the first term 23 and the term -4 is -4 - 23 = -27. So, that tells us that the term -4 is -27/-3 = 9 terms away from the first term. So the answer is 10.
Another approach is simply to list out the pertinent terms of the sequence:
23, 20, 17, 14, 11, 8, 5, 2, -1, -4. Here it's really clear that n is 10 when tn is -4.
Rey
2 posts Page 1 of 1