How to practice reverse memory

I am reading a book about the astronaut selection process and one of the quizzes is as follows:

You need someone to read number sequences like the ones below, and then you have to recite the numbers backwards.

a) 2 0 4
b) 3 4 6 1
c) 8 2 0 7 2
d) 6 2 7 3 3 9

For example, I would listen exercise a) and I would have to repeat 4 0 2. The quiz gets more difficult as you progress, because the numbers keep increasing.
My question is How would you prepare (train) for this?

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It depends on the amount of digits and what you want to do. If it is 8 digits for example and you mainly want to pass these questions, then I would simply visualize the numbers as I process them verbally. To process them in reverse, I would simply read backwards from my visualized string.

If it is something alike 30+ digits, in this case I would use a digit system and put the digits in a memory palace. Then I would traverse the memory palace journey backwards (this is actually a lot easier). In doing so I would be able to recall the digits backwards quite reliably.


Thanks for the quick reply Nagime!! I forgot to mention that you have 10 seconds per question, can you do all this in 10 seconds?

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Visualize the numbers that are being read in 10 seconds provided there are not too many? Yes.

Visualize a memory palace and place digits into it using an image system within 10 seconds? Yes.

To expand a bit. The former is almost instant, it would take maybe under 0.2 seconds.

The latter takes a lot more training for a good rate.

You can get very much quick enough at each of these.

The world records for example are under 14 seconds for memorizing a pack of cards and 547 digits at a rate of a digit a second. That is not quite to say that you have to aim for the world record but for both speed and stability it goes quite a long way.

Particularly, if you have less digits to memorize, you may be able to sacrifice some stability for a higher rate.