If the speed is increased by 25%, that is, the efficiency is 5: 4, then the time required is 4: 5.
If 1/5 can be advanced, then 3x* 1/5=3 and x=5, that is, the original time is 4*5=20 hours.
The latter part is accelerated by 20%, that is, the efficiency is 6: 5, and the required time is 5: 6.
If 1/6 can be advanced, then the original time of the latter part is 2÷( 1/6)= 12 hours.
The original time of the first 200 parts is 20- 12=8 hours.
The original hourly rate is 200÷8=25.
Number of parts: 25×20=500.