The radius of the Earth is 6.37×1000000 m and its average dencity is 5.517×1000kg/m×m×m.calculate the mass of earth to correct significant figures.
mass= density*volume
= density*4/3*PI* r^3
= 5.517E6*4/3*PI* (6.37E6)^3
= 5.97323898e27 kg according to google calc.
for your problem, nmber sig figures is three.