Final answer:
To find the greatest possible total number of different students who could have registered for these courses, add the number of students who registered for each subject and then subtract the number of students who registered for both English and Mathematics. The greatest possible total is 773.
Step-by-step explanation:
To find the greatest possible total number of different students who could have registered for these courses, we need to add the number of students who registered for each subject and then subtract the number of students who registered for both English and Mathematics.
Greatest Possible Total = (Number of students registered for English) + (Number of students registered for History) + (Number of students registered for Mathematics) - (Number of students registered for both English and Mathematics)
Greatest Possible Total = 442 + 187 + 234 - 90
Greatest Possible Total = 773