A calculator displays a result as 1.3540980 107 kg. the estimated uncertainty in the result is ±2%. how many digits should be included as significant when the result is written down?
Let's see what the range of possible values you can have for 1.3540980 if your uncertainty is +/- 2%
2% of 1.3540980 = 0.02 * 1.3540980 = 0.027082
So the lowest possible value for your result is
1.3540980 - 0.027082 = 1.327016
The largest possible result is
1.3540980 + 0.027082 = 1.38117996
Notice that only the 1st 2 digits of the result match which is reasonable since a 2% error means that your result is only accurate to within 1 part in 50.