A series is given below which contains a wrong term. (4c – a – 10) , (3b + a – 1) , (bc + a – 1) , (ac + 7b) , (ab + ac + bc + 18) , (3b2 + ac – 21) Note: 'a', 'b' and 'c' are single-digit natural numbers, greater than 1, such that only 'b' is prime and (a < c <
b) . Find the wrong term of the series.

Case I: when 'b' = 2 No values are possible for 'a' and 'c' So, this case is invalid. Case II: when 'b' = 3 Only number less than 3 but more than 1 is 2. But we have 'a' and 'c'. So, this case is invalid. Case III: when 'b' = 5 Only possible value for 'a' or 'c' = 4 as both 2 and 3 are prime. So, this case is invalid. Case IV: when 'b' = 7 Possible values = 4, 6 So, 'a' = 4 and 'c' = 6 So, this case is valid. On putting values of 'a', 'b' and 'c' in the series, We get; Series: 10, 24, 45, 73, 112, 150 10 + (7 x 2) = 24 24 + (7 x 3) = 45 45 + (7 x 4) = 73 73 + (7 x 5) = 108 108 + (7 x 6) = 150 (ab + ac + bc + 18) is the wrong term of the series. Hence, option b.