Memoriad Additions: how to solve it quickly?

So, I would like to solve quickly this two-column digits, instead of solving 1 column by 1 column.

But additions appear to be more difficult to solve this way. Do you have some good idea to help me solve it quickly?

Thanks in advance.

@bjoern.gumboldt I tag you cause I know you have participed in Mental Math World Cup if I remember correctly, and any advice would be very pleasant to me.


Did you try using complements?

Your first number is 58 and the second number will make you go past 100, so just take the 38 and subtract it from 58 instead to get to 20 and don’t forget the 1 in front of it now, so really 120. The complement of 84 is 16, so subtract that for 20 - 16 = 4 and you got 204.

The next 90 just go on top of that. Luckily the 3 and 7 in the unit digits are complements, so add 1 to 4 + 2 in the tenth digits and then 20 on top of that. You’re at 294 now. Then it’s minus 11 again, etc.

@Kinma has written more about it in this post…

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If I understood well the method is this [correct me if I´m wrong]:

We take the complement of 62, that is, 38. We subtract now 58 - 38, which gave us 20, and we add 100, that is, 120.

We proceed the same with other numbers.


You professionals calculators always amazes me.

THANK YOU VERY MUCH @bjoern.gumboldt

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@bjoern.gumboldt But isn’t Finger Math Method better than the method you share it?

Look at this girl, it’s fantastic. She completed the Memoriad Additions Task with the Finger Method:

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What do you think she does differently?

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I don’t know exactly what she’s doing with her fingers :confused:

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Check the video at 0:45 just before she types the answer and you’ll see that her left index finger is down (1) and all fingers of her right hand are down (9).

You can also change the playback speed to 0.25 and pause the video as needed, you’ll see that she’s basically using her fingers like a soroban.


I want to calculate like her but I don’t know how doing it.

I´m training with fingers but I have many issues, perhaps it is just a phase before mastering it.

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How do you train something that you don’t know how to do though?

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Here is a video that explain how to count with fingers.
I don’t know if this is exactly the way she does it, but it looks very similar.


The girl uses the same method. Keep in mind that she uses her fingers to set the subtotals. She needs to keep the hundreds in her head though. However; she can - and I see that she does not do this this - put the carry on one hand while typing the 2 digits subtotal.

From 0:10 she clears her fingers, then sets 12 on her fingers, then adds 63.