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What should come in place of the question mark (?) in the given series? 305 251 206 170 143 ?
130
125
120
115
125
Calculate the differences between consecutive terms: the differences themselves form a decreasing series of prime numbers or squares/cubes, but here the differences are 54, 45, 36, 27, which are multiples of 9.
Calculate the differences between consecutive terms: the differences themselves form a decreasing series of prime numbers or squares/cubes, but here the differences are 54, 45, 36, 27, which are multiples of 9.
Analyze Differences
Calculate the difference between consecutive numbers: 305-251=54, 251-206=45, 206-170=36, 170-143=27.
Identify Pattern
The differences are 54, 45, 36, 27. These are multiples of 9 decreasing by 9 each time (9x6, 9x5, 9x4, 9x3).
Calculate Final Term
The next difference must be 9x2 = 18. Subtracting this from the last term gives 143 - 18 = 125.
A: 130 is incorrect as it implies a subtraction of 13, not 18. C: 120 is incorrect as it results from subtracting 23. D: 115 is incorrect as it results from subtracting 28.
B is correct because the series follows a pattern of subtracting consecutive multiples of 9, leading to 143 - 18 = 125.
In number series, if the numbers are decreasing steadily, always check the difference between consecutive terms first. If differences aren't constant, look for arithmetic progressions within the differences themselves.
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