Introduction
Tuyet's mirror image of the labelling of the columns leads her to believe that it is the rightmost column which determines the size of the decimal number, in the same way that the leftmost column does for whole numbers.

Comments: Text in italics
Interviewer: Text in red
Tuyet: Text other colour

Interviewer:
I have a number that starts 3 point something something and you get to choose the rest of the number.

Interviewer:
Here are the cards to choose from marked 0,1,2,3,4,5,6,7,8 and 9. I'm going to ask you to make the biggest number that you can by choosing any two of these cards.

Tuyet:
I'll pick the 9 and then the 8.

Tuyet makes 3.89

Interviewer:
OK What were you thinking when you made this choice?

Tuyet:
9 hundreds and 8 tens is the most I can make.

Interviewer:
If I swapped the 8 and the 9 around, would I make it bigger or smaller?

Tuyet:
Smaller, as there'd only be 8 hundreds.

Interviewer:
OK, let's put those cards back...

Interviewer:
...and could you make another number, this time as small as you can?

Tuyet:
I'll need the zero and the one.

Tuyet makes 3.10

Interviewer:
OK, so this time you've got...

Tuyet:
no hundreds and only one ten

Interviewer:
So if I swapped the 0 and the 1 around would it get bigger or smaller?

Tuyet:
Bigger, because swapping would make one hundred. Now there are no hundreds, just a ten.