(10,287.56 - 10,005.23) / 10,287.56 =
(282.33) / 10,287.56 = 0.0274
0.0274/100 = 2.74%
At the beginning of the day, the dow jones index was at $10,287.56. at the end of the day, the dow jones index was at $10,005.23. The rate of change of the dow jones on this particular day is 2.74%