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Find the missing number in the series: 4, 9, 19, 39, 79, ?
159
158
160
149
159
Multiply each term by 2 and add 1 to get the next term in the sequence (2x + 1 pattern).
Multiply each term by 2 and add 1 to get the next term in the sequence (2x + 1 pattern).
Analyze consecutive differences and multiples
Examine the growth rate of the series: 4 to 9 is +5 or 42+1; 9 to 19 is +10 or 92+1; 19 to 39 is +20 or 192+1; 39 to 79 is +40 or 392+1.
Apply the rule to find the missing term
Since each term follows the rule multiplying by 2 and adding 1, apply this to the last given term: 79 * 2 + 1 = 158 + 1 = 159.
B: 158 is wrong because it misses the +1 addition after multiplying 79 by 2. C: 160 is incorrect due to a calculation error. D: 149 is wrong because it underestimates the progression.
A is correct because multiplying the last term 79 by 2 and adding 1 results in 159.
Always check for mixed operations like double-and-add or double-and-subtract when number series grow at an exponential rate.
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