Mental Maths for Numerical Reasoning Tests: The Shortcuts Worth Learning
Percentage change, ratios, reverse percentages and estimation, done at the speed a numerical reasoning test requires. The handful of shortcuts that pay for themselves in one sitting.
Look at where the time goes on a numerical reasoning question. The calculation is the smallest slice. Most of the minute disappears into finding the right two numbers in a table with fourteen rows, and most of the marks are lost by candidates who found the right numbers and then took twenty seconds doing arithmetic that should have taken five. Both are fixable, and the arithmetic half is the easier fix.
Why a calculator does not solve this
Many numerical tests permit a calculator, and candidates conclude that arithmetic speed does not matter. Two problems with that. Some of the most common tests, including the Criteria CCAT and the Thomas Aptitude battery, do not allow one at all. And even where a calculator is allowed, reaching for it has a fixed cost of several seconds, which is a bad trade on a calculation you could have done in three.
The rule that follows is simple: calculate mentally by default and reach for the calculator only for genuinely multi-step work. To make that viable you need about six techniques.
The six that pay for themselves
Finding the figures faster
This is the bigger half of the time budget and it gets almost no attention in preparation material.
The skip decision, which depends on the vendor
There is no universal rule here and getting it wrong is expensive.
- No penalty for wrong answers: SHL, Criteria, Wonderlic and most conventional batteries. A blank and a wrong answer score identically, so guess on anything you cannot solve and never leave an item empty. With four options, a guess has a positive expected value; a blank has none.
- Marks deducted for wrong answers: the Aon cut-e scales family and the Thomas Aptitude battery. Here a guess has a negative expected value unless you can eliminate options. If you cannot rule out at least two, skip it.
- Response time recorded without a visible clock: Sova, and to a degree Korn Ferry Talent Q. Nothing tells you to hurry and your pace is scored anyway, so the discipline is to commit rather than to circle back.
Establishing which of those three you are in, before you start, is worth more than any arithmetic shortcut on this page. If you do not know, work out which provider sent your test first.
A twenty-minute drill that actually works
Reading shortcuts does nothing. They have to become automatic, and automatic means retrieved without deliberation. A drill that gets there faster than generic practice:
- Five minutes of percentage building. Random three-digit numbers, find 15, 35 and 60 per cent of each, out loud, no writing. Stop when it feels boring; boring is the target state.
- Five minutes of percentage change. Pairs of numbers, compute the change both ways. Deliberately notice that going from 80 to 100 is a 25 per cent rise while going from 100 to 80 is a 20 per cent fall. That asymmetry is a distractor on real papers.
- Five minutes of reverse percentages. The one everybody gets wrong under pressure, and the one with the most reliable distractor.
- Five minutes of estimation against options. Take real practice items and answer them by estimation alone, then check. You will be right more often than feels responsible, and that is the point.
What to do the week before
Drill for four or five short sessions rather than one long one, then do a full-length timed run of the actual format two days before. Doing the timed run last matters: the shortcuts need to be automatic before you test them under pressure, or the run just teaches you that you are slow.
The numerical reasoning practice covers the standard formats, and the week-before plan puts this in order alongside everything else.