Introduction
In this interview, Ricardo shows that he thinks 9 tenths is larger than 98 hundredths. He knows that 3.9 is the largest one decimal place number he can make and that 3.98 is the largest two decimal place number, but he thinks all amounts of tenths are larger than all amounts of hundredths. His wrong way of thinking allows him to correctly choose 3.01 as the smallest number.

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

Interviewer:
I have a number that starts 3 point something something...

Interviewer:
...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.

Ricardo selects the 9 card only and makes 3.9

Interviewer:
OK. What about if I asked you to use two of the cards this time?

Ricardo adds the 8 after the 9.

Interviewer:
OK let's compare those two numbers...3.9 and 3.98. Which one's bigger?

Ricardo:
The 3.9 is bigger because it's 9 tenths.

Interviewer:
and the 3.98?

Ricardo:
It's 98 hundredths and they're smaller

Ricardo thinks any number of tenths is larger than any number of hundredths.

Interviewer:
OK, now we'll put those cards back ...and could you make another number, this time as small as you can?

Ricardo:
One hundredth would be the smallest

Ricardo has no difficulty making the smallest number, as he believes hundredths are smaller than tenths and then chooses just one.