The answer is 3. The only common factor between the numbers is 3, because 15 is 3 times 5, while 9 is 3 times 3.
Step-by-step explanation:
4 for a pen
7 for 1 note book
1. False because a rational is a fraction or part of a number (

).

2. True; a real number is any number that isn't imaginary (

)
3. True; same reason
4. True; an integer is any number that can be wrote without a fraction or decimal (the opposite of rational).
5. True;

and that's a decimal.
6. True; the natural number system starts from 0 and counts upwards
7. True; reason above
Answer:
83
Step-by-step explanation:
17 correctly answered questions x 5 points = 85 points
3 blank questions x 0 points = 0 points
5 wrong questions x -2 = -10 points
85 - 10 = 75 points
75 + 8 = 83