# 99547 / 89318

Up to 4 decimal places
I almost got the fifth decimal but the countdown of the recording software broke my concentration. It’s a 5 minute video so I advice to speed it up or skip to the end, haha. I’ve had faster times, like 5 decimals in 3 minutes but I unfortunately didn’t record those. The most decimals I’ve calculated has been 13 decimals, which took me 10-15 minutes. I am going to look for another recording software, this one only records for 5 minutes so I can calculate to 10+ decimals and record it.

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If you’re trying to record your screen, check out OBS (free).

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Out of interest, are you doing this by dividing by 8, 9 or 89 and then performing a form of cross-multiplication? Or simply by calculating multiples of 89318 and subtracting them?

If it’s the latter, I’d recommend exploring other methods. I solve this by dividing the remainders by 89 and adjusting the other digits accordingly by cross-multiplication, and I believe that is the fastest for advanced calculators.

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Hi Daniel,
I think the latter is ok if get familiar with it, since the calculation amount are almost the same.

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I calculate the multiples of 89318 and subtract, yes.

Thanks, but I am not interested in other methods or getting much faster. Most people can’t even hold both 99547 and 89318 in their head, so the fact that I can calculate an answer to 10+ decimals is enough for me.

Can you explain how you would calculate 99547/89318 with the criss-cross method? I didn’t know the criss-cross method can be used for division.

That is quite impressive that you can solve this by subtracting multiples of 89318, since it is stretching the capacity of the working memory to hold the required remainders.

However at a point, you need to switch to the criss-cross method when the denominator gets too large! The size of the numerator is actually irrelevant, since you just process one new digit at a time.

The method is complicated to explain but I’ll try my best to explain it briefly:

99 / 89 = 1 rem 10 (answer is 1.___)
10 & next digit (5) gives 105
subtract cross multiplication between answer and remaining digits of divisor (318) just gives 1x3 in this case: 105 - 1x3 = 102

102/89 = 1 rem 13 (answer is 1.1___)
13 & next digit (4) gives 134
134 - 1x1 (from first digit of answer) - 1x3 (from second digit of answer) = 130

130 / 89 = 1 again lol rem 41 (answer is 1.11___)
41 & next digit (7) gives 417
417 x 1x8 - 1x1 - 1x3 = 405

405 / 89 = 4 rem 49 (answer is 1.114__)
49 & next digit (0 because we’ve run out) gives 490
490 - 1x8 (2nd digit of answer) - 1x1 - 4x3 = 469

469 / 89 = 5 rem 24 (answer is 1.1145__)
24 => 240
240 - 1x8 - 4x1 - 5x3 = 213

213 / 89 = 2 rem 35 (answer is 1.11452…)
etc.

Hope that helps Try it for some examples and with a little practice, you can probably get 10 digits in these questions in a couple of minutes.

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WOW!

That is such a big difference!

It’s insane how much easier that is! I could calculate to 5 decimals in less than 30 seconds with that method!

Does it also work for something like 4578312÷9683259? Does the size of the divisor, in this case 9683259, matter?

Why do schools not teach things like this to people?
This is amazing.

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Never mind, it works for 4578312÷9683259!

In 20 seconds I got 0.472, wow!

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bc schools don’t care how you learn, but cares how good your results are?¿ Joke, I know there are many good teachers, might be just luck you didn’t encounter them yet. Like Danield must be a keen teacher.

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First of all, Johnny, amazing that you can do this!
Chapeau!

@Daniel_360, great technique!
I did not know about it.

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Same here ,

I read this technique somewhere but I forgot where I read this and that time I didn’t actually understand .

Then I came here , and now I understood but only half of the technique and rest of the part is still unclear for me.

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Какъв софтуер ползвате за това деление,моля?Или приложение?

This is the website

http://windhoff.net/mental_arithmetic/#Multiplication

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Благодаря!

If you look up some Vedic maths - they call this the Flag method see

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The method I use for solving these is cross-division, and I’ve just published a full explanation of how it works: https://worldmentalcalculation.com/how-to-divide-by-long-numbers-in-mental-math/

Hope that helps! Let me know if something there is not clear.

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