One hundred astronomers are asked to measure the luminosity of Venus.
The results, rounded off to the nearest 10 units, are as follows:

   No. of astronomers    Luminosity measured
   ------------------    -------------------
      2                    160 units
      5                    170 units
      6                    180 units
      9                    190 units
     15                    200 units
     30                    210 units
     20                    220 units
      7                    230 units
      3                    240 units
      3                    250 units

Based on these observations only, answer the following questions.
(a) What is your best estimate of the luminosity of Venus?
(b) What is the full width at half maximum (FWHM) of these measurements?
(c)  What is the approximate margin of error for the luminosity of Venus?