Q20. A vernier callipers has 20 divisions on the vernier scale, which coincides with $19 { } ^ { \text {th } }$ division on the main scale. The least count of the instrument is 0.1 mm . One main scale division is equal to $\_\_\_\_$ mm.\\
(1) 0.5\\
(2) 2\\
(3) 5\\
(4) 1