Given that the measurement in the diameter of the radius is with a least count of 0.01cm
Here is a proof we know that r =2cm d = 4+/-0.01m now divide both the sides by 2 we r = 2+/-0.005 cm
Now the second Question
d =1.95cm+/-0.01cm Now divide by 2 on both the sides consider the number 1.95cm since the digit 1 and 9 are a certain number therefore it is significant Where as the other .95 digits are not uncertain therefore they are not classified under the category of significant digits
So according to the rule I have written d/2 = 0.975+/-0.005cm but now wait for moment we have only one significant figure to start off Now only the last digit in 0.975
now we have to round off the digit 5 because on starting our significant figures were only 2 d =0.98+/-0.005