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Feed of \( 2000 \) kg/h contains \( 3 \) per cent foreign matter. If the cleaner removes \( 54 \) kg/h of it, the cleaning efficiency is

  • A.27 per cent
  • B.97 per cent
  • C.90 per cent
  • D.60 per cent

Answer: C

Correct answer: 90 per cent

Find the foreign matter present, then the fraction removed:

\[ 2000 \times 0.03 = 60\ \mathrm{kg/h\ foreign\ matter} \]

\[ \frac{54}{60} \times 100 = 90\ \mathrm{per\ cent} \]

The distractor \( 2.7 \) per cent would express the removal as a fraction of the whole feed, which measures nothing useful. Cleaning efficiency must always be referred to the impurity present, since the same 54 kg removed from a much dirtier feed would represent a far poorer performance.

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