Explanation:
Let the initial diameter be do.
Diameter after the first pass d1 = 0.6 do
Diameter after the second pass d2 = 0.7 d1 = 0.7 × 0.6 do
Thus, the ratio of final to initial diameter is:
\(\frac{{{d_2}}}{{{d_o}}} = 0.7 \times 0.6 = 0.42\)
The overall reduction will be 1 – 0.42 = 0.58 = 58%