>>She is in 5th grade and this is her homework...
>>
>>So, what if it were 28.5 * 1.843? Then 28 * 1.8? 29 * 2? What are the rules? What is significant?
>
>For quick rounding, I would keep ONE significant digit in most cases.
>
>28.5 * 1.843 --> 30 * 2
>
>The idea is to keep the first digit in each number, and replace all other digits with zeroes - rounding the next digit up or down, as appropriate.

Ok, a couple examples to make sure I understand:

 4.008 * 2.09 ------> 4 * 2
38.002 * 0.49 ------> 38 * .5
61.203 * 0.42 ------> 61 * .4
 0.98  * 7.61 ------> 1 * 8 (not sure about the 0.98 going to 1 on this one)