KRN in the DLR Test: Mental Arithmetic

Of all the modules in the DLR basic assessment, KRN is probably the one where preparation pays off most directly: pure mental arithmetic. No notes, no calculator, no space on screen to jot down intermediate steps — just a spoken question and an empty input field. If you reach for a calculator constantly in everyday life, you'll quickly notice here how rusty your mental math has become.

The good news: mental arithmetic is a skill that improves noticeably within a few weeks of focused practice — far more so than, say, raw reaction speed. This article covers what KRN actually measures, how scoring works, the most common mistakes, and — as the centrepiece — concrete calculation techniques for the main task types: breaking numbers apart, rounding and adjusting, percentage shortcuts, units, and speed-time-distance, each with its own worked examples.

If you'd first like an overview of all the modules in the basic assessment, you'll find one in the DLR Test: The Complete Guide.

What is KRN?

KRN stands for mental arithmetic (Kopfrechnen) and is part of the computer-based performance tests within the DLR certificate examination stage 1. It tests the ability to solve arithmetic problems purely mentally — no paper, no calculator, under time pressure, and without any visual support from the question itself.

The module therefore tests more than pure calculation skill. It's also about taking in information while already beginning to process it, holding intermediate results in mind, and staying resilient under time pressure. In an aviation context this isn't an academic exercise: fuel reserves, speeds, times and distances sometimes need to be estimated quickly in the cockpit, often without a calculator at hand.

Format and procedure

The questions are read aloud only — the screen typically shows just an input field, not the numbers of the question itself. So you have to listen, understand and begin calculating simultaneously, rather than being able to look at the question again visually.

In terms of content, KRN covers several task types: multi-digit basic operations (addition, subtraction, multiplication, division), chained calculations with several steps in sequence, percentage calculations, unit conversions, and questions on speed, time and distance. Input happens via an on-screen keyboard where the OK key can change position — the keyboard layout is shuffled, so pure "muscle-memory typing" doesn't work and you actually have to look before confirming.

In DLR Exam Trainer, KRN is split into three difficulty levels that combine different task types and levels of complexity. As with all modules, every question is freshly generated.

What really counts: scoring

Scoring is based on the proportion of correctly solved questions. The traffic light in DLR Exam Trainer shows green from 85% correct, yellow from 70%. These values are based on publicly known experience reports and are meant as orientation.

It's important to understand: what counts isn't just whether you enter the right number at the end, but how reliably you do that under time pressure across an entire series of questions. A single brilliantly solved chained calculation doesn't help much if three simpler questions afterwards fail on input errors or carelessness. Consistency across different task types therefore matters more than peak performance on a single type.

TipActively use the input field as external memory — type intermediate results in as soon as they're ready, instead of holding them in your head as well while you keep calculating.

The most common mistakes

Holding intermediate results in your head instead of the field

A common mistake is holding several intermediate steps in mind at once, even though the input field could already be used. That ties up capacity unnecessarily that's then missing for the next calculation step. As soon as a partial result is settled, it should be typed in — not "remembered".

Not noticing the shuffled keyboard

Because the OK key changes position, automated "blind typing" quickly leads to input errors despite a correctly calculated result. That's particularly frustrating because the calculation itself is right, but the entry gets counted as wrong.

Not converting units cleanly

With questions involving units (for example kilometres and metres, hours and minutes), it often happens that the calculation is correct but the wrong unit is given, or a conversion step gets forgotten. The result is often numerically close but still counts as wrong.

Confusing base value and percentage value in percentage questions

A classic mistake is applying the percentage to the wrong reference value — for instance subtracting a discount from the wrong starting price, or confusing an increase with a decrease. Under time pressure this happens surprisingly often, even with otherwise simple percentage calculations.

Rearranging the speed-time-distance formula incorrectly

The basic formula speed = distance ÷ time is well known, but under pressure it sometimes gets rearranged incorrectly for the quantity being asked for, for example when time is asked for instead of distance. Without clean written notation — which is missing here by design — this mix-up happens faster in your head than you'd expect.

Mental-math techniques for the main task types

Breaking numbers apart

Breaking a number apart means splitting it into simpler components so you calculate in several easy steps instead of one hard one. Instead of calculating 47 × 6 directly, break 47 into 40 + 7 and calculate 40 × 6 = 240 and 7 × 6 = 42, giving 282 together. This also works for subtraction: 83 − 27 can be calculated as 83 − 20 − 7, which is 63 − 7 = 56.

Example: 58 × 7. Broken apart: 50 × 7 = 350, 8 × 7 = 56, together 406.

Rounding and adjusting

Rounding and adjusting means rounding a number up or down to a "clean" value and then correcting for the difference. This is especially useful for subtractions with awkward numbers. Instead of calculating 91 − 38 directly, round 38 up to 40 (plus 2) and calculate 91 − 40 = 51, then add the 2 back = 53.

Example: 154 − 69. Round 69 up to 70 (plus 1): 154 − 70 = 84, then add 1 = 85.

Percentage shortcuts

Most percentage questions can be reduced to simple fractions: 10% is one-tenth (just shift the decimal point one place left), 50% is half, 25% is a quarter, 1% is one-hundredth. Combinations of these solve most everyday percentage problems. For 15%, calculate 10% plus half of that (5%).

Example: 15% of 240. 10% of 240 = 24, 5% (half of that) = 12, together 36.

Example: An item costs 80 francs and the price rises by 20%. 20% of 80 is 16 (10% = 8, doubled = 16), so the new price is 80 + 16 = 96 francs.

Units

For unit questions, it helps to have fixed conversion factors ready automatically: 1 km = 1000 m, 1 h = 60 min, 1 min = 60 s. The important thing is to convert first and only then calculate, rather than "hoping" at the end that the unit already fits.

Example: How many metres does someone cover in 15 minutes at a speed of 4 km/h? First convert 4 km/h to m/min: 4000 m ÷ 60 min ≈ 66.7 m/min. Then multiply by 15: roughly 1000 m.

Speed, time, distance

The three formulas speed = distance ÷ time, time = distance ÷ speed, and distance = speed × time should be internalised well enough that you can rearrange them for the quantity being asked without conscious thought. A simple rule of thumb: if the quantity you're solving for stands alone on one side, multiply the other two; if it's in the denominator of the base formula, divide.

Example: A plane covers 300 km in 2.5 hours. Speed = 300 ÷ 2.5 = 120 km/h.

Example: At 90 km/h, how long does a distance of 135 km take? Time = 135 ÷ 90 = 1.5 hours, so 1 hour 30 minutes.

ImportantThese worked examples are original practice questions created to illustrate the techniques, not actual DLR test questions.

Concrete training tips

Memorise squares and cubes

Knowing the squares of numbers up to 30 and the cubes up to 10 by heart saves valuable seconds and calculation steps on many questions. It's plain rote work, but it pays off across practically every task type.

Consistently use the input field as external memory

Train yourself to type in intermediate results as soon as they're settled, instead of also holding them in your head. That frees up working memory for the next calculation step.

Deliberately watch for the shuffled keyboard

Practise specifically with an input layout where key positions change, so you don't develop the habit of blindly tapping a fixed position.

Practise by task type separately first

Train percentage calculations, unit conversions, and speed-time-distance questions separately at first, before mixing them. That way you can more precisely identify which task type is still giving you trouble.

Short, regular sessions rather than rare long ones

Mental arithmetic benefits strongly from short, frequent repetition. A few minutes daily achieves more over several weeks than a single long session on the weekend.

Use the error analysis deliberately

DLR Exam Trainer shows you after every session which task type had the most mistakes. Use that information to target your training on your weak spot, rather than practising a little of everything evenly.

Fitting KRN into your preparation

KRN is one of six modules that can be tried free for three days, one session per day, before Pro is required. The app's three difficulty levels build on each other, and the adaptive level recommendation automatically suggests the next level once you've completed three sessions in a row green — or a level lower after two in a row red.

For structured preparation across several weeks that plans KRN sensibly alongside the other modules, the 8-Week Training Plan is worth a look. In the exam simulation, incidentally, KRN comes right after PHY and before RMS — two modules that also demand concentration under time pressure, which is why it's worth practising KRN not just in isolation but also right after other demanding tasks.

If you're also curious how nervousness affects performance in modules like KRN, it's worth reading DLR Test Stress & Mindset. And since KRN and RMS both rely on auditory processing under time pressure, training often complements well with RMS: Running Memory Span in the DLR Test.

With DLR Exam Trainer you can practise KRN in freshly generated variations every time, so you're preparing for the technique behind the questions rather than for individual tasks.