Answer:
In total there are 50 students.
Explanation:
Since in a group of students 20 study account, 21 study mathematics, 18 study history, 7 study account only, 10 study mathematics only, 6 study account and mathematics only and 3 study mathematics and history only, to determine how many student are there altogether the following calculation must be performed:
7 + 10 + 6 + 3 = 26
Account = 20 - 7 - 6 = 7
Mathematics = 21 - 10 - 6 - 3 = 2
History = 18 - 3 = 15
26 + 7 + 2 + 15 = X
50 = X
Therefore, in total there are 50 students.