Number series: how to find the rule

Lesson 4 of 20 in Union Aptitude Prep. It plays free, with no account.

Union Aptitude PrepNumber series: find the rule The setupA number series gives you a row and asks for the next number. Don’t stare at the numbers. Look at the gaps.Write the gapsThree to five is plus two. Five to nine is plus four. Then plus eight, then plus sixteen.The ruleThe gaps double every time. That is the rule for this series.

The lesson, in words

Where patterns fit

You can meet number patterns in Algebra and Functions. The official sample includes a number-pattern question.

The setup

A number series gives you a row and asks for the next number. Don’t stare at the numbers. Look at the gaps.

Write the gaps

Three to five is plus two. Five to nine is plus four. Then plus eight, then plus sixteen.

The rule

The gaps double every time. That is the rule for this series.

Your turn · 45 s

3, 5, 9, 17, 33, ?

Answer: 65. The next gap is 32, so 33 + 32 = 65. 66 is the trap if you just double the last number.

Next lesson: Arithmetic and geometric series

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