Least count ,LC=1MSD−1VSD
Here 10VSD=9MSD or 1VSD=(9/10)MSD
Thus, LC=(1−9/10)1MSD=1/10×0.1cm=0.01cm (as 1MSD=0.1cm from diagram)
From diagram, main scale reading, MSR=4.3cm and vernier scale reading, VSR=7 (because division 7 coincide with any line on main scale )
The diameter of the metal ball =MSR+(VSR×LC)=4.3+(7×0.01)=4.37 cm
Radius of the ball =4.37/2=2.185 cm=2.18 cm