The main scale of a vernier callipers is calibrated in mm and 19 divisions of main scale are equal in length to 20 divisions of vernier scale. In measuring the diameter of a cylinder by this instrument, the main scale reads 35 divisions and the 4th division of vernier scale coincides with a main scale division. Find radius of cylinder.

Explanation

To find the radius of the cylinder using the vernier calipers, we can follow these steps:

### Step 1: Understand the relationship between the main scale and the vernier scale.
According to the problem, 19 divisions of the main scale (MS) are equal to 20 divisions of the vernier scale (VS). This means:
\[ 19 \, \text{MSD} = 20 \, \text{VSD} \]

### Step 2: Calculate the length of one vernier scale division.
From the relationship established, we can express one vernier scale division in terms of the main scale division:
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