In the series given below, one number does not fit. Find that number.
3, 5, 13, 44, 177, 891
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 44
The terms grow faster and faster, so compare each term with the one before. The rule is multiply by 1, 2, 3, 4, 5 in turn and add 2, 3, 4, 5, 6 in turn:
\(3\times1+2=5\)
\(5\times2+3=13\)
\(13\times3+4=43\), but the series has 44
\(43\times4+5=177\), which matches the next term
\(177\times5+6=891\)
The term after it fits only if the fourth term is 43; with 44 it would be \(44\times4+5=181\). So 44 does not fit the series.