didieravoaka wrote: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
t(n) = t(n) - 3.
According to the formula above, each term is 3 less than the preceding term.
The result is an EVENLY SPACED SET.
The value of n when t(n) = -4 is equal to the NUMBER OF TERMS when the biggest term is 23 and the smallest term is -4.
To count the number of integers in an evenly spaced set, use the following formula:
(biggest - smallest)/interval + 1.
The
interval is the distance between successive terms.
Here, the interval is 3, since each term is 3 less than the preceding term.
Since the biggest term = 23 and the smallest term = -4, we get:
Number of terms = (biggest - smallest)/interval + 1 = [23 - (-4)]/3 + 1 = 10.
The correct answer is
C.
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