>>>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)
>

For quick estimates, just keep ONE significant digit. Convert all non-zero digits except the first to zero; if the digit dropped is 5 or more, increase the first digit by one (for rounding). The first example is correct, the second, I would change to 40 * 0.5 (notice the rounding); the third, to 60 * 0.4.

The fourth example, once again, is correct: rounding to 1 s.d. means, in this case, rounding to the closest 0.1; 0.98 is closer to 1.0 than to 0.9. Or just look at the algorithm in the previos paragraph (the 8 is dropped, 0.9 is increased to 1.0).