Mathematics
JAMB 2017
What is the next number in the series 2, 1, \(\frac{1}{2}\), \(\frac{1}{4}\)...
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A.
\(\frac{1}{3}\)
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B.
\(\frac{2}{8}\)
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C.
\(\frac{3}{7}\)
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D.
\(\frac{1}{8}\)
Correct Answer: Option D
Explanation
2, 1, \(\frac{1}{2}\), \(\frac{1}{4}\).....
There are 4 terms in the series
Therefore the next number will be the 5th term
T
n = ar\(^{n − 1}\) (formular for geometric series)
a = first term = 2
r = common rate = \(\frac{\text{next term}}{\text{previous term}}\) = \(\frac{1}{2}\)
n = number of terms
T
5 = 5th term = ?
T
5 = ar\(^{5 - 1}\)
= ar\(^4\)
= 2 × (ar\(^{n − 1}\))
4
= 2 × \(\frac{1}{16}\)
= \(\frac{1}{8}\)
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