Number Classification Notes & Questions | Class 3 Reasoning | Drishti OS

Number Classification

What you'll learn

Group numbers by a shared property: even, odd, or multiples.
Spot the number that breaks the rule.
Use simple checks — division and counting — to confirm.

Key concepts

Level 1 — Core idea

Verbal: Even numbers end in 0, 2, 4, 6, 8. Odd numbers end in 1, 3, 5, 7, 9. Multiples of a number can be reached by counting up in equal steps.

Symbolic: n is even if n ÷ 2 has no remainder; n is a multiple of k if n ÷ k has no remainder.

Visual: Think of counting in twos (2, 4, 6, 8...) — every number you land on is even; the ones you skip are odd.

Level 2 — Going deeper

A number can belong to more than one group (12 is even AND a multiple of 3). When classifying, find the rule that fits three of the four numbers, then check the fourth breaks only that rule.

NCERT anchor

NCERT Math Mela, Class 3 — Chapters on odd/even and multiplication support this classification skill through skip counting and grouping.

Worked example

Which number does NOT belong: 6, 8, 9, 10?

Step 1 — 6, 8, 10 are all even numbers.
Step 2 — 9 is odd, not even.
Answer: 9

Which number does NOT belong: 3, 6, 10, 9?

Step 1 — 3, 6, 9 are all multiples of 3.
Step 2 — 10 is not a multiple of 3.
Answer: 10

Common mistakes

Mistake	Why	Fix
Mixing up even and odd	Rushed check	Divide by 2 and look for a remainder
Missing a multiple	Skip counting error	List the multiples first: 3, 6, 9, 12...
Picking by size, not rule	Largest/smallest bias	Always check the property, not the size
Forgetting to check all four	Stopping early	Test every number against the rule

Quick check

Which does NOT belong: 12, 14, 15, 16?
Which does NOT belong: 5, 10, 20, 22?
Which does NOT belong: 4, 8, 12, 15?
Stretch: Which does NOT belong: 21, 24, 27, 29 (multiples of 3)?

Revision tip: Write the rule in one short sentence before choosing the odd number.

Open the Practice tab for graded questions on Number Classification.

Number Classification