Choosing Seconds and Count for Flash Mental Math: A Seconds-per-Number Chart
When someone says “ten 2-digit numbers in 5 seconds”, it’s hard to picture straight away how fast each number flashes. The difficulty of flash mental math is mostly decided by the “seconds per number”: the total seconds divided by the count. This article covers how to work out seconds per number with a chart, rough guides for each speed band, and how to choose conditions that suit you.
Seconds per number = total seconds ÷ count
Flash mental math conditions are usually stated as three things: digits, count and seconds. The seconds generally means the time to show all the numbers. To find how long each number is on screen, divide the total seconds by the count.
Converting to seconds per number also lets you compare conditions with different counts on the same scale. “Ten 1-digit numbers in 3 seconds” and “fifteen 2-digit numbers in 5 seconds” are both around 0.3 seconds per number, so they flash at almost the same speed. The difference lies in the digits and how long you must hold the total.
Seconds-per-number chart (counts of 3–30 × 2–15 seconds)
Here are common combinations of count and total seconds converted to seconds per number, rounded to two decimal places.
| Count \ Total | 2 s | 3 s | 5 s | 8 s | 10 s | 15 s |
|---|---|---|---|---|---|---|
| 3 | 0.67 s | 1 s | 1.67 s | 2.67 s | 3.33 s | 5 s |
| 5 | 0.4 s | 0.6 s | 1 s | 1.6 s | 2 s | 3 s |
| 10 | 0.2 s | 0.3 s | 0.5 s | 0.8 s | 1 s | 1.5 s |
| 15 | 0.13 s | 0.2 s | 0.33 s | 0.53 s | 0.67 s | 1 s |
| 20 | 0.1 s | 0.15 s | 0.25 s | 0.4 s | 0.5 s | 0.75 s |
| 30 | (raised to 3 s) | 0.1 s | 0.17 s | 0.27 s | 0.33 s | 0.5 s |
This site’s flash mental math tool won’t go faster than 0.1 seconds per number, so that the device’s screen can keep up. Trying to set 30 numbers in 2 seconds would be about 0.067 seconds each, so the total is raised to 3 seconds (0.1 seconds each). The settings panel shows “… per number” underneath, so you can check without looking at the chart.
Rough guides for each speed band
Splitting speeds into bands by seconds per number, roughly as follows, makes it easier to see what level you’re practicing at. These are only practice guides and don’t correspond to exam grades or ranks.
| Per number | How it feels | Suited to |
|---|---|---|
| 2 s to 1 s | You can read the number and add it calmly | Just starting out, or right after moving up a digit |
| 1 s to 0.6 s | Reading takes too long; you need to add as soon as you see it | Building rhythm |
| 0.6 s to 0.3 s | You can’t keep up unless you take in numbers as shapes | Intermediate; abacus-style mental math starts to pay off |
| 0.3 s to 0.2 s | Visible only for an instant | Advanced; a battle against missed numbers |
| Under 0.2 s | Close to an afterimage | Top-level practice |
A number isn’t on screen for its whole slot. In this tool, about 72% of each slot shows the number and the rest is blank, so at 0.5 seconds per number, the number is visible for about 0.36 seconds. The blank also stops two identical numbers from looking like one (and the tool never shows the same number twice in a row anyway).
How to choose conditions that suit you
- 1
Choose the digits
Practice with 1 digit until you can reliably answer ten 1-digit numbers at around 0.3 seconds each. If your abacus school has set a target, match those digits.
- 2
Choose the seconds per number
Find the speed at which you get 7–8 out of 10 right. Getting every one right isn’t “just right”; it’s a sign the speed is too slow.
- 3
Choose the count and work out the total
Seconds per number times the count is the total seconds. At 0.4 seconds per number, enter 4 seconds for 10 numbers and 6 seconds for 15.
When you raise the digits, it’s safest to go back to 1 second or more per number for a while. Even at the same 0.5 seconds, 2 or 3 digits give you more to take in, so what worked for 1 digit won’t be fast enough. The thinking behind the order for raising conditions is covered in detail in how to practice flash mental math.
Seconds per number for the 20 Level-challenge levels
The tool’s Level challenge gives addition-only problems at the following 20 levels. Listing the seconds per number shows how it slows down again each time the digits go up.
| Level | Conditions | Per number |
|---|---|---|
| 1–2 | 1 digit, 3 numbers, 6 s / 4 s | 2 s / 1.33 s |
| 3–5 | 1 digit, 5 numbers, 6 s / 4 s / 3 s | 1.2 s / 0.8 s / 0.6 s |
| 6–8 | 1 digit, 10 numbers, 6 s / 4 s / 3 s | 0.6 s / 0.4 s / 0.3 s |
| 9–11 | 2 digits, 3 numbers, 5 s; 2 digits, 5 numbers, 6 s / 4 s | 1.67 s / 1.2 s / 0.8 s |
| 12–13 | 2 digits, 10 numbers, 8 s / 6 s | 0.8 s / 0.6 s |
| 14–15 | 2 digits, 15 numbers, 8 s / 5 s | 0.53 s / 0.33 s |
| 16–17 | 3 digits, 5 numbers, 6 s; 3 digits, 10 numbers, 8 s | 1.2 s / 0.8 s |
| 18–20 | 3 digits, 15 numbers, 10 s / 5 s / 3 s | 0.67 s / 0.33 s / 0.2 s |
FAQ
- Is the time in flash mental math per number or for the whole problem?
- It’s generally the total time to show all the numbers. Seconds per number is the total divided by the count: ten 2-digit numbers in 5 seconds is 0.5 seconds each. Schools sometimes state it differently, so it’s worth checking when you’re given conditions.
- What level is 0.5 seconds per number?
- For 1 digit, it’s a speed with no time to read the number out; you have to add it as soon as you see it. Think of it as the entry point to intermediate. At 0.5 seconds per number with 2 or 3 digits, there’s more to take in, so it gets considerably harder.
- Why don’t numbers appear when I set a very fast speed?
- Every device has a limit to how fast it can redraw the screen, and at extreme speeds it may move on without displaying a number. That’s why the flash mental math tool automatically raises the total seconds so it never goes faster than 0.1 seconds per number.
- Can I practice at the same speed as an exam?
- Yes. In Free settings you can combine digits (1–4), count (2–30) and seconds (0.5–60). Exam conditions vary by organization and grade, so check the conditions published by the organization you’re taking it with before entering them.
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