The third of geometric progression (G.P) is 10 and the sixth term is 80. Find
FURTHER MATHEMATICS
WAEC 2010
The third of geometric progression (G.P) is 10 and the sixth term is 80. Find the common ratio.
- A. 2
- B. 3
- C. 4
- D. 8
Correct Answer: A. 2
Explanation
\(T_{n} = ar^{n - 1}\) ( Geometric Progression)
\(T_{3} = ar^{3 - 1} = ar^{2} = 10 .... (1)\)
\(T_{6} = ar^{6 - 1} = ar^{5} = 80 .....(2)\)
Divide (2) by (1)
\(r^{5 - 2} = r^{3} = 8 \)
\(r = \sqrt[3]{8} = 2\)
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