The probability of the treatment group mean being lower than control groups mean by 15 points or more will be 0.027.
Based on the information given, let the assumption that the frequency for the points greater than 15 include 20, 4, and 3 while the entire population is 1000.
Then, the probability of the treatment group mean being lower than control groups mean by 15 points or more will be:
= (20 + 4 + 3)/1000
= 27/1000
= 0.027
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