In the series given below, one number does not fit. Find that number.
4, 6, 15, 49, 203, 1011
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 203
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:
\(4\times1+2=6\)
\(6\times2+3=15\)
\(15\times3+4=49\)
\(49\times4+5=201\), but the series has 203
\(201\times5+6=1011\), which matches the last term
The last term fits only if the fifth term is 201; with 203 it would be \(203\times5+6=1021\). So 203 does not fit the series.