Select the option that will replace the question mark (?) in the following…
2019
Select the option that will replace the question mark (?) in the following series. 121, 129, 156, 220, ?
- A.
356
- B.
296
- C.
345
- D.
300
Attempted by 147 students.
Show answer & explanation
Correct answer: C
Key idea: look at the differences between consecutive terms; they form cubes of consecutive integers.
Compute the differences: 129 − 121 = 8 = 2^3; 156 − 129 = 27 = 3^3; 220 − 156 = 64 = 4^3.
Next difference is 5^3 = 125.
Add this to the last given term: 220 + 125 = 345.
Answer: 345 is the missing number.
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