How the Cijferreeksen test works
Each of the 28 items is a row of numbers built on one rule, ending in a gap. You work out the rule and choose the next number from five options, only one of which is right. You may use scrap paper; the instructions mention no calculator.
You have 15 minutes. LTP tells candidates not to worry about not reaching every series, because the test is designed that way. Only correct answers count and nothing is deducted, so LTP advises answering every question even when unsure.
The same item type appears inside the G-test, and LTP also uses the Cijferreeksen test as the retest when a numerical score needs a second look. LTP keeps several versions of the paper at different levels.
How to find the rule
Check these in order. Most series give up their rule by the third step:
- Differences: write the gap between each pair of neighbours. A constant gap is the simplest rule.
- Differences of differences: if the gaps grow, look at how they grow. They may rise by a fixed amount or double.
- Ratios: try times 2, times 3 or halving.
- Two steps in turn: a series can alternate, such as times 2 then minus 2.
- Two series woven together: compare the odd positions and the even positions separately.
- Sums: each number may be the sum of the two before it.
Worked examples
5, 10, 8, 16, 14, ? Options: 12, 20, 24, 28, 30. The steps alternate: times 2, minus 2, times 2, minus 2. The next step is times 2, so the answer is 28.
3, 4, 7, 11, 18, ? Options: 25, 27, 29, 30, 36. The gaps (1, 3, 4, 7) have no fixed pattern, but each number is the sum of the two before it: 3 + 4 = 7, 4 + 7 = 11, 7 + 11 = 18. So the next is 11 + 18 = 29.
Tips for the real Cijferreeksen test
- Keep scrap paper ready and write the differences under each series rather than holding them in your head.
- Before you choose, check your rule on the last two numbers in the series, not just the first few.
- Give a series about half a minute. If the rule has not appeared, pick the most likely option and move on.
- Answer every series before the 15 minutes run out. A guess can score; a blank cannot.
- LTP’s free practice site has a four-minute number series test.
Practise the Cijferreeksen test on CogniPrep
Our version matches the live length: 28 series on one 15-minute clock with five options each, from easier to harder, with Back, Next and an overview. The series are generated fresh each sitting. You get your number correct and a 1 to 9 practice score against people practising here.