(2.34+7.9)/4.25
would this be 2.4 or 2.41??
would you do 2.34+7.9= 10.24/4.25=2.41
or would you say it's 2.4 b/c 7.9 only has 2 sig figs.
or would you say 2.34+7.9 = 10.2/4.25=2.40
If it were my decision, I would go with 2.41, because you would be limiting yourself to about 4% accuracy by throwing out the last significant figure. Although the 7.9 has only two significant figures, it is accurate to within about 1.3%. The numerator of the fraction is even more accurate, about 1%.
The way the subject is taught, however, they may want you to say that
2.34 + 7.9 = 10.2/4.25 = 2.4, because the 7.9, which dominates the numerator, has only two significant figures.
If you go through the error analysis in a rigorous way, you would end up with the answer being about 2.41 +/- 0.02