Wang Ming can complete 12 mental arithmetic problems in 3 minutes. Now it takes him only 2 minutes to complete 12 mental arithmetic problems, and his speed of mental arithmetic has increased by several percent

Wang Ming can complete 12 mental arithmetic problems in 3 minutes. Now it takes him only 2 minutes to complete 12 mental arithmetic problems, and his speed of mental arithmetic has increased by several percent

Do 4 questions a minute, improve to 6 questions a minute
So (6-4) / 6 = 50%