100.0 g x 1.00 cal/g x Celcius x 28.6 degrees celcuis
I need to multiply all of these and use significant numbers.
I think the number would be 3000, but how do I label it?
First, we should have it in a way that is visually easier to understand:
$\displaystyle (100.0g)\left(1.00\frac{cal}{g*Celsius}\right)(28. 6 \ Celsius)$
We first multiply the first two terms in the analysis:
$\displaystyle \left(100.\frac{cal}{Celsius}\right)(28.6 \ Celsius)$
Notice that the 100.0 lost it's 0 because 1.00 has 3 significant digits and therefore 100 also has to have three sig digs, since 100.0 has 4 significant digits, then we keep the decimal and lose the zero to get 3 significant digits. Now we multiply the other two numbers:
$\displaystyle \left(100.\frac{cal}{Celsius}\right)(28.6 \ Celsius) = 2860 \ cal$
You can use 2860 because both 100. and 28.6 have 3 significant digits, and 2860 has 3 as well, therefore the answer works.