The odd word in a group

Learning outcome

Name the class shared by three words, then mark the word that is outside that class.

Concepts and reasons

A classification item gives four words. Three belong together. The answer is the one that does not. Decide the class from the three, not from a story about the fourth.

Useful classes in this lesson are fruit against a vegetable, root against a stem tuber, and metal against a non-metal. Potato is a stem tuber, so it is outside a group of root vegetables. Carbon is a non-metal, so it is outside a group of metals.

Worked examples

Example 1. Apple, mango, banana, potato. Apple, mango and banana are fruits. Potato is not a fruit. Potato is the odd word.

Example 2. Carrot, radish, beetroot, potato. Carrot, radish and beetroot are roots. Potato is a stem tuber. Potato is the odd word.

Common traps

Do not stop at "all are foods". That class includes every option, so it cannot produce an odd one. Use the narrowest class that still holds three words.

Practice questions

1. Iron, copper, silver, carbon. Which word is outside the class?
2. Why is "all are found in the kitchen" a useless class for apple, mango, banana and potato?

Answers and explanations

1. Iron, copper and silver are metals. Carbon is a non-metal, so carbon is the odd word.
2. The class is true of all four words, so it does not separate one of them.

Analogy

Apple, mango, banana, potato.

Three are fruits. Potato is the one that is not. The class is "fruit", and the odd word is potato.

Quick reference

• Find a class that fits exactly three words.
• A class that fits all four words does not answer the question.
• Potato is a stem tuber, not a root and not a fruit.
• Carbon is the non-metal in a list of metals.