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?

>Perhaps not exactly fifth-grade... but the reasoning is to maintain one significant digit in each number. Thus, 4.28 would be rounded to 4, and 4.28 million to 4 million.
>
>When adding or subtracting, at what place you round (tens, hundreds...) is more relevant, but when multiplying or dividing, the number of significant digits is the relevant part.
>
>>This is a sample problem out of a math workbook. I get that "estimating" essentially means performing calculations on rounded values, but they are mixing the places they round to in the example below. Why isn't it either 1 x 4 or 0.8 x 4.2? Not quite getting how they are doing that. I thought with rounding, you had to know the place you wanted to round to in order to have the product be valid.
>>
>>

>>Estimate Decimal Products
>>-------------------------
>>
>>Estimate 4.2 x 0.843
>>
>>  0.843 -------->   0.8
>>x   4.2 -------->  x  4
>>                   ====
>>              about 3.2
>>
>>Both factors are rounded
>>down. The actual product
>>is greater than 3.2.
>>