Reasoning - Odd Man Out

In every competitive exam, Odd Man Out type questions are very common. In odd man out problems all the items given in the question except one follow a certain pattern or a group. The item which is different and doesn’t belong to that group will be the answer.

Problems of this type are categorized under the head of CLASSIFICATION. That means out of the all given elements, one will not fall into the group due to some difference in the property. That is the odd element.

For Example −

Type 1 −

Which one of the words given below is different?

a - Mango

b - Apple

c - Potato

d - Cherry

e - Blackberry

Explanation − Except potato, all the rest are the names of the fruits, while Potato is a vegetable. Hence, it is the odd one.

Type 2 −

Find out the pair which is different.

a - Cow and Buffalo

b - Cock and Hen

c - Horse and Mare

d - Dog and Bitch

e - Peacock and Peahen

From the above, the second one is the feminine of the first one except the first pair. So the answer will be (a).

These types of problems are classified into 3 categories. That are −

• Alphabet Classification
• Word Classification
• Number Classification

Let’s discuss about the above types of classifications.

Alphabet Classification

In this type, a group of messed letters consisting 3 letters are kept together. The pattern in which they are grouped is to be analysed and we have to find which group out of this have the same pattern or relationship between the letters. The choice which doesn’t follow that pattern will be the right answer.

For Example − Find the odd man out.

a - ZW

b - TQ

c - SP

d - NL

e - PM

Solution − Z^-3W, T^-2Q, S^-3P, N^-2L, P^-3M

So the answer will be NL, which is choice (d).

Word Classification

In this type, different items which belong to common properties like places, parts of speech, professions, etc. are present. The one which doesn’t match to that category will be the odd one.

For Example − Find the odd one among the following.

a - Mercury

b - Moon

c - Jupiter

d - Saturn

e - Venus

Solution − Here, choices (a), (c), (d) and (e) belong to one group because these all are Planets. But moon is a satellite. So moon will be the right answer.

Number Classification

Number classification means a group of numbers which follows the same pattern. In this case we will see that there are numbers given in question from which we have to find the odd one. The numbers may belong to a particular set i.e. they may be odd, even, prime, rational, cubes, squares, coded binary digits etc. One choice will not follow the rule and that will be our answer. The following steps are required to analyse the question.

• Check the basic logic first

  • Whether is there any connection between the given numbers?

  • Whether any particular number is connected to all the numbers?

  • Classification of assumed numbers

  • Unless you find the odd one in the initial step, then jump to step 2

• Check the Squares and Cubes

  • also check Squares +1s and Cubes +1s

    If you can't find the odd one in step 2, then go to step 3

• Try remaining Mathematical Possibilities like tables, divisibility rules. If you are not able to find any link among given options, try to catch out correlation among the digits of every number it encounters.

For Example − Find the odd among the following.

a - 1011

b - 1101

c - 1111

d - 10001

e - 111

Solution − These numbers follow the binary coding. Let’s convert them into decimal.

1011 = 1 × 2³ + 0 × 2² + 1 × 2¹ + 1 × 2⁰

= 8 + 0 + 2 + 1

= 11

1101 = 1 × 2³ + 1 × 2² + 0 × 2¹ + 1 × 2⁰

= 8 + 4 + 0 + 1

= 13

1111 = 1 × 2³ + 1 × 2² + 1 × 2¹ + 1 × 2⁰

= 8 + 4 + 2 + 1

= 15

10001 = 1 × 2⁴ + 0 × 2³ + 0 × 2² + 0 × 2¹ + 1 × 2⁰

= 16 + 0 + 0 + 0 + 1

= 17

111 = 1 × 2² + 1 × 2¹ + 1 × 2⁰

= 4 + 2 + 1

= 7

Here, choice (d) will be the answer because 15 is not a prime number but all others are prime numbers.