Roasted copper ore containing the copper as \( \mathrm{CuSO}_{4} \) is to be extracted in a countercurrent stage extractor. Each hour a charge consisting of 10 tons of gangue, 1.2 tons of copper sulphate, and 0.5 ton of water is to be treated. The strong solution produced is to consist of \( 90 \% \mathrm{H}_{2} \mathrm{O} \) and \( 10 \% \mathrm{CuSO}_{4} \) by weight. The recovery of \( \mathrm{CuSO}_{4} \) is to be \( 98 \% \) of that in the ore. Pure water is to be used as a fresh solvent. After each state, 1 ton of inert gangue retains 2 tons of water plus the copper sulphate dissolved in that water. Equilibrium is attained in each stage. How many stages are required?