Task: Question Answering
Input (English): Sentence: Mechanical pulping yields almost a tonne of pulp per tonne of dry wood used, which is why mechanical pulps are sometimes referred to as "high yield" pulps. With almost twice the yield as chemical pulping, mechanical pulps is often cheaper. Mass-market paperback books and newspapers tend to use mechanical papers. Book publishers tend to use acid-free paper, made from fully bleached chemical pulps for hardback and trade paperback books. 
Question: How many times more yield does the mechanical pulping process produce when compared to to the chemical pulping process?
Output (English): twice