Number Series Notes & Questions | Class 4 Reasoning | Drishti OS

Number Series

Spot the rule that connects numbers in a list.
Find the next number by continuing the rule.
Work with patterns that add, subtract, double, or grow by a growing gap.
Recognise special patterns like square numbers and sum-of-two-before patterns.

If every number is a fixed amount more than the last one (like +2, +2, +2), just add that same amount again.

Sometimes the gap itself grows: +1, then +2, then +3, then +4. Look at how the gap changes before finding the next number.

Each number can be double the one before it (x2 each time).

Some patterns are built by adding the two previous numbers together: 1, 1, 2, 3, 5, 8 ...

NCERT anchor: CBSE Class 4 logical reasoning; Math-Magic 4 Ch 12 — patterns in numbers

Find the next number: 3, 6, 9, 12, ?

Step 1 — Gap between each number = 3.
Step 2 — Add 3 to the last number: 12 + 3 = 15.
Answer: **15**

Find the next number: 1, 2, 4, 7, ?

Step 1 — Gaps are +1, +2, +3.
Step 2 — Next gap should be +4.
Step 3 — 7 + 4 = 11.
Answer: **11**

Mistake	Why it happens	Fix
Assuming the gap never changes	Some patterns have a growing gap	Check at least three gaps before deciding
Adding instead of doubling	Missed a x2 pattern	Compare ratios, not just differences
Stopping after one correct guess	Pattern may need more terms to confirm	Verify the rule works for all given numbers
Mixing up sum-of-two-before with simple addition	Both involve "adding"	Check if each term uses the previous two numbers, not just one

5, 10, 15, 20, ? — what is next?
2, 4, 8, 16, ? — what is next?
1, 3, 6, 10, ? — what is the growing-gap rule here?
Stretch: In 1, 1, 2, 3, 5, 8, what are the next two numbers, and what rule do they follow?

Revision tip: Write the gaps between numbers on a line below the series — the gap pattern often reveals the rule instantly.

Open the Practice tab for graded questions on Number Series.