Dolomite ore is a mixture of Calcium and Magnesium carbonate, It is leached with concentrated sulfuric acid to recover Magnesium as Magnesium sulphate. Dolomite contains 25% calcium, 15% magnesium and 5% silica. After leaching, the soluble matter is filtered off and the solids are washed. The washed solids are analysed and found to contain 2% silica, 0.5% Mg and 1% Al. Compute the % of Mg extracted by acid leaching.