Find the odd one out in the given series.5, 20, 50, 80, 125, 180

The correct answer is Option (2) → 50

Every term is a multiple of 5; dividing by 5 gives 1, 4, 10, 16, 25, 36, which are the squares 1, 4, 9, 16, 25, 36 except for one. So each term is \(5n^2\):

• \(5\times1^2=5\)

• \(5\times2^2=20\)

• \(5\times3^2=45\), but the series has 50

• \(5\times4^2=80\)

• \(5\times5^2=125\)

• \(5\times6^2=180\)

50 does not follow the rule, so 50 is the odd one out.