Largest possible difference between two numbers

Question

I came across this practise question for a government numeracy test:

What is the largest possible difference between 10 & 20 to 2 decimal places?

What is the answer? As far as I can tell, the difference between 10 and 20 does not have a largest or smallest solution, but only one, which is equal to 10.

Answer 1

Here's a possible interpretation.

Looking at the quiz linked in comments to the OP we find the following questions, with Q21 being the question from the OP:

19. What is the smallest number to 2 decimal places that can be rounded to 20?
20. What is the largest number to 2 decimal places that can be rounded to 20?
21. What is the largest possible difference between 10 & 20 to 2 decimal places?

I think that Q21 is meant to follow from the answers to Q19 and Q20, but the questions are badly worded and open to interpretation.

Is $19.50$ the answer to Q19 (the smallest number to two decimal places that rounds to the integer $20$)? Or is it $19.995$ (the smallest number that, when rounded to two decimal places, gives $20.00$)?

Similarly, does Q20 give $20.49$ or $20.00499999...$?

Suppose we take the first alternative in both cases, with the equivalent answer for the value $10$. Then I think the intended answer for Q21 would be:

$20.49-9.50=10.99$.

I do think the question is intended to highlight rounding up and rounding down. It just does so very poorly.

Answer 2

The best I can read it is to say there are two possible differences, $+10.00$ and $-10.00$ and $+10.00$ is larger. I agree it is badly worded.