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Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Select the missing number: 5, 10, 20, 40, ?
60
80
100
50
80
Observe that each term is double the previous term; the common ratio is 2 (x2 pattern).
Observe that each term is double the previous term; the common ratio is 2 (x2 pattern).
Analyze the series
Look at the differences and multipliers between consecutive terms: 5 to 10 (5 multiplied by 2), 10 to 20 (10 multiplied by 2), 20 to 40 (20 multiplied by 2).
Apply the pattern
To find the missing term, continue the geometric progression by multiplying the last known term (40) by the common ratio (2): 40 * 2 = 80.
A: 60 is incorrect as it follows an addition of 20, not multiplication. C: 100 is incorrect as it would require a multiplication factor of 2.5. D: 50 is incorrect as it would require adding 10, breaking the consistent multiplication pattern.
B is correct because the series follows a geometric progression with a constant ratio of 2, where 40 multiplied by 2 equals 80.
If a series grows rapidly, always check for multiplication or squares/cubes first instead of addition.
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