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WBCS Preliminary Examination 2021 — General Studies · Question 178 of 200

Q178
ArithmeticNumber Series & Progressions
Given set (7, 77, 140) then follows
  1. a.(9, 88, 180)
  2. b.(6, 66, 120)
  3. c.(8, 80, 166)
  4. d.(4, 10, 160)

Answer: (B) (6, 66, 120)

In (7, 77, 140) the second number is $7\times11=77$ and the third is $7\times20=140$, i.e., the pattern is $(n,\ 11n,\ 20n)$. Only (6, 66, 120) fits: $6\times11=66$ and $6\times20=120$. Check the others: for 9 it should be (9, 99, 180), for 8 it should be (8, 88, 160), and for 4 it should be (4, 44, 80). Each wrong option gets at most one term right to tempt you, so verify both relations.

Q177 Whole paperQ179