The Thanksgiving tradition started between the British colonies and the Native Americans. Hence, we base only on those two nationalities. Then,
English: 100 - 80 = 20
Native Americans: 100 - 75 = 25
The total would be 20 + 25 = 45. There are a t least 45 people from all three heritages.
I hope I was able to help you. Have a good day.