Q20. While measuring diameter of wire using screw gauge the following readings were noted. Main scale reading is 1 mm and circular scale reading is equal to 42 divisions. Pitch of screw gauge is 1 mm and it has 100 divisions on circular scale. The diameter of the wire is $\frac { x } { 50 } \mathrm {~mm}$. The value of $x$ is :\\
(1) 21\\
(2) 142\\
(3) 71\\
(4) 42