Solution: This manuscript has X characters, so it takes x/60 to type 60 words per minute. When it takes two fifths, the efficiency is improved by 50%. So the required time is 2/5 * (x/60)+3/5 * x/(60 * (1+50%)) = x/75. At this time, it was completed half an hour in advance, so x/75+30=x/60, and the solution: x=9000, so this manuscript.