How Ixly Cijferreeksen works
Each question is a row of numbers with a question mark, and you choose the number that belongs there. Ixly’s own example multiplies the first number by six, the second by five, the third by four and the fourth by three, so the fifth has to be multiplied by two. Other items add or subtract an amount that grows or shrinks, multiply by a constant, or hide two series in one row so that each skips a place.
The test is adaptive: a right answer brings a harder question and a wrong one an easier question, and the test stops once your level is measured precisely enough. In the ACT you get 10 to 17 questions. Each subtest opens with an example with an explanation and three practice questions with no clock; on those, you only see whether your answer was right.
Every question then has 45 seconds. An unanswered question counts as wrong, you cannot go back, and leaving the test does not stop the clock: the time runs on to the next question.
How to solve an Ixly number series
Work through the rule types in the order Ixly’s own example suggests:
- Write the differences between neighbouring numbers. A constant or steadily changing difference solves most easy items.
- If the numbers grow fast, divide each by the one before. A fixed or falling multiplier, like Ixly’s 6, 5, 4, 3, shows up straight away.
- If the row zigzags, read every other number. Two series woven together is a type Ixly names.
- Check the rule against every number before you look at the options, then pick the one it produces.
Worked examples
Series: 3, 18, 90, 360, 1080, ? The numbers grow fast, so divide: 18 ÷ 3 = 6, 90 ÷ 18 = 5, 360 ÷ 90 = 4, 1080 ÷ 360 = 3. The multiplier falls by one each step, so the next is 2 and the answer is 2160.
Series: 5, 12, 8, 10, 11, 8, ? The differences go up and down, the sign of two hidden series. The 1st, 3rd and 5th numbers (5, 8, 11) rise by 3; the 2nd, 4th and 6th (12, 10, 8) fall by 2. The question mark is 7th, in the rising series, so the answer is 14.
Tips for the real Cijferreeksen
- Have a scratch pad ready. Ixly allows one, and writing differences is faster than holding them in your head.
- Use the three practice questions to settle in. They have no clock, and the real 45 seconds start after them.
- Always answer before the time runs out. A blank is marked wrong, so a guess can only help.
- Take any break between subtests, never during one. The clock keeps running even if you close the test.
- Read a sten score of 5 as average, not a fail. Ixly’s manual says so in as many words.
- Check the test language in your invitation. Ixly lists Cijferreeksen among its least language-dependent tests.
Practise Cijferreeksen on CogniPrep
Our Cijferreeksen game uses our own bank of number series with four options. It adapts over 10 to 14 questions, starting just below average as Ixly’s does, with 45 seconds a question; you select an answer and press Submit, with no going back. Your result is a practice percentile shown as a sten from 1 to 10, from a score that weighs the level you reached, your accuracy and any time-outs.