A multiple disc clutch is to transmit $15 \mathrm{~kW}$ at $750 \mathrm{rpm}$. The inner and outer radii of the friction surfaces are $60 \mathrm{~mm}$ and $100 \mathrm{~mm}$, respectively. The coefficient of friction is 0.1 and the maximum allowable pressure is $350 \mathrm{kPa}$. Assuming uniform wear, the number of pair of contact surfaces required is_______

A multiple disc clutch is to transmit $15 \mathrm{~kW}$ at $750 \mathrm{rpm}$. The inner and outer radii of the friction surfaces are $60 \mathrm{~mm}$ and $100 \mathrm{~mm}$, respectively. The coefficient of friction is 0.1 and the maximum allowable pressure is $350 \mathrm{kPa}$. Assuming uniform wear, the number of pair of contact surfaces required is_______

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