Datavio interview questions

1. One pandas library related question to deal with null values in dataframe. 2. One basic SQL related 3. One aptitude

There are 25 horses among which you need to find out the fastest 3 horses. You can conduct a race among at most 5 to find out their relative speed. At no point, you can find out the actual speed of the horse in a race. Find out the minimum no. of races which are required to get the top 3 horses.