Question

Craig measured a length as 0.034 millimeters. What is the margin of error?

Answer 1

it's a little hard to explain without giving it away but basically you go to the next digit after the last significant digit

for example, since you have 0.034 you go to 0.034x where x is the next place a significant digit could be

now, for rounding rules, remember that if the digit is 5 or greater you round up

so 0.0335 would be the smallest number that rounds up to 0.034
and 0.034499999 (etc) would be the biggest number that rounds down to 0.034