Odd Man Out and Series
Find the odd one out in number series
Odd Man Out and Series problems test your ability to identify patterns in sequences of numbers, letters, or figures. In 'Odd Man Out' questions, you must identify the element that doesn't follow the established pattern. In 'Series' questions, you need to find the next or missing term by recognising the underlying rule governing the sequence.
Key formulas and rules
Key concepts
Arithmetic Series
In an arithmetic series, each term is obtained by adding or subtracting a fixed number (common difference) from the previous term. Example: 3, 7, 11, 15, 19... (common difference = 4). To identify: calculate the difference between consecutive terms. If the difference is constant, it's an AP.
Geometric Series
In a geometric series, each term is obtained by multiplying or dividing the previous term by a fixed number (common ratio). Example: 2, 6, 18, 54, 162... (common ratio = 3). To identify: divide each term by the previous term. If the ratio is constant, it's a GP.
Squares and Cubes
Many series are based on perfect squares or cubes. Recognise squares: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144... Recognise cubes: 1, 8, 27, 64, 125, 216, 343, 512, 729, 1000... Some series may add/subtract a constant to squares/cubes.