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What number comes next in the sequence: 4, 9, 19, 39, ?
79
78
81
80
79
Observe that each number is approximately double the previous one, following the formula: Term * 2 + 1.
Observe that each number is approximately double the previous one, following the formula: Term * 2 + 1.
Analyze the relationship between consecutive terms
Calculate the difference or multiplier between terms: 4 to 9 is (4 * 2) + 1 = 9; 9 to 19 is (9 * 2) + 1 = 19; 19 to 39 is (19 * 2) + 1 = 39.
Apply the logic to find the missing term
Following the established pattern of (Previous Term * 2 + 1), multiply 39 by 2 and add 1. Calculation: 39 * 2 = 78, and 78 + 1 = 79.
B: 78 is the result of just multiplying 39 by 2 without adding the increment of 1. C: 81 is incorrect as it follows neither the +1 increment pattern nor any standard growth sequence here. D: 80 is incorrect because it is simply 39 * 2 + 2, breaking the constant rule of +1.
A is correct because the sequence follows a consistent mathematical rule of multiplying the previous number by 2 and adding 1 to reach the subsequent term.
When terms roughly double in size, always test the n*2 + k pattern before checking for complex differences between terms.
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