Final answer:
The total number of students is the sum of students from both universities, which equals 35.
Step-by-step explanation:
To calculate the total number of students from both Oxford University and Ibadan University who visited UDS, we simply need to add the two quantities together. There were 15 students from Oxford and 20 students from Ibadan. To find the total, we perform the following calculation:
Number of Oxford students + Number of Ibadan students = Total number of students
15 + 20 = 35
The correct answer is (a) 35 students.