Direction : Series I: 8, 9, 15, 25, 42, 68, 105 Series II: 60, 180, 450, 900,…
2020
Direction : Series I: 8, 9, 15, 25, 42, 68, 105
Series II: 60, 180, 450, 900, 1350, 1380, 675
If wrong term in series II is ‘N’, then which statement is true about (N/30 +1)?
(i) It’s a prime number.
(ii) Sum of the digits is less than 9.
(iii) It’s a nearest multiple of 5 and its remainder is 4.
Answer: C. Only (i) follow — ConceptA wrong-number series follows ONE fixed generating rule; the wrong term is the single value that breaks that rule. For a multiplicative series the test…
- A.
Only (ii) and (iii) follow
- B.
Only (i) and (ii) follow
- C.
Only (i) follow
- D.
None follow
- E.
All (i), (ii) and (iii) follow
Attempted by 5 students.
Show answer & explanation
Correct answer: C
Concept
A wrong-number series follows ONE fixed generating rule; the wrong term is the single value that breaks that rule. For a multiplicative series the test is the ratio of each term to the one before it — in a clean series these ratios form their own regular pattern. Once the wrong term N is found, evaluate the requested expression and then test each given statement as an independent true/false claim.
Application — find the wrong term
Series II: 60, 180, 450, 900, 1350, 1380, 675. Take successive ratios (each term ÷ previous term):
180 ÷ 60 = 3
450 ÷ 180 = 2.5
900 ÷ 450 = 2
1350 ÷ 900 = 1.5
the multipliers are decreasing by 0.5 each step (3, 2.5, 2, 1.5, …), so the next multiplier must be 1, giving 1350 × 1 = 1350
the value printed in that slot is 1380, not 1350 — this is the term that breaks the rule
Check the rule still holds afterward: the final multiplier should be 0.5, and 1350 × 0.5 = 675, which matches the last printed term. So the corrected sequence is 60, 180, 450, 900, 1350, 1350, 675, and the wrong term is N = 1380.
Application — evaluate the expression
Substitute N = 1380 into (N / 30 + 1):
1380 ÷ 30 = 46
46 + 1 = 47
Cross-check — test each statement about 47
Statement (i), primality — 47 is a prime number: its only divisors are 1 and 47, so this claim is true.
Statement (ii), digit total below 9 — the digits of 47 add to 4 + 7 = 11, and 11 is not below 9, so this claim is false.
Statement (iii), remainder 4 on division by 5 — the exam wording "nearest multiple of 5 and its remainder is 4" is read as the division test: 47 ÷ 5 gives quotient 9 and remainder 2, not 4, and 47 is not itself a multiple of 5 either, so this claim is false on both readings.
Result
Only the primality claim, statement (i), is true of the evaluated value, so the selection that names primality alone is the one that follows.