A→5QB→5QC→5Q
A1,A2,A3,A4,A5B1,B2,B3,B4,B5
C1,C2,C3,C4,C5
A1A2A3B1C1⇒C13×C35×C15×C15=750, where three questions are picked from any of the subject and one each from other two subjects.
A1A2B1B2C1⇒C23×C25×C25×C15=1500, where one question is picked from one of the subject and two each from rest of the two subjects.
∴Total number of ways=2250