Mechanical Operations
The value of work index does not change materially from one equipment to another. If the value of work index determined for close circuit grinding is Wi, then the same for open circuit grinding will be

1.34 Wi
Wi
0.5 Wi
3.34 Wi

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Mechanical Operations
Pick out the wrong statement pertaining to the roll crushers.

For hard material's crushing, the reduction ratio should not exceed 4
Both the rolls run necessarily at the same speed
Maximum feed size determines the required roll diameter
Reduction ratio and differential roll speed affect production rate & energy consumed per unit of surface produced

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