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Find the missing number in the series: 4, 9, 19, 39, 79, ?
158
159
160
161
159
Observe that each term is generated by doubling the previous number and adding 1: (Term * 2) + 1.
Observe that each term is generated by doubling the previous number and adding 1: (Term * 2) + 1.
Analyze the pattern
Observe the progression: (4 * 2) + 1 = 9, (9 * 2) + 1 = 19, (19 * 2) + 1 = 39, and (39 * 2) + 1 = 79.
Apply pattern to find the next term
Following the rule (Previous Term * 2) + 1, calculate for the last term: (79 * 2) + 1 = 158 + 1 = 159.
A: 158 is the result of just doubling 79 without adding 1, C: 160 is derived from an incorrect addition, D: 161 is derived by adding 3 instead of 1.
B is correct because the series follows the recursive formula x(n) = 2 * x(n-1) + 1, resulting in 79 * 2 + 1 = 159.
If the numbers in a series grow at an accelerating rate, always test multiplying the previous term by 2 or 3 before checking addition-based differences.
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