text: this is a significant digits/ rounding question for chemistry, what does this number become when rounded to... ok, it is the element lanthanum, it's mass # is 138.9055. what does this become when rounded to 2 digits (the 100ths place). my chemistry teacher wants it rounded to the 100ths place, but sometimes i get problems where it is for example: 157.9482. does this become 157. 95, or does it become 157.95, and then upt to 158 because of the 5 uping the 9 to make it 158.00.  anywho, my main question is what does the original become(one at the top) it becomes 138.91  when asked for significant digits or when using scientific notation, the starting number is rounded up or down before truncating (making shorter).