IMO Practice Test — Factors & Multiples
6 Questions • 12 min • Olympiad level
12:00
Question 1 of 6
medium
How many prime numbers are there between 10 and 20?
3
4
5
2
Explanation: 11, 13, 17, 19 → four primes.
Question 2 of 6
hard
The sum of the first three prime numbers is…
9
10
11
6
Explanation: 2 + 3 + 5 = 10.
Question 3 of 6
medium
Which number is a factor of every whole number?
0
1
2
10
Explanation: 1 divides every number.
Question 4 of 6
hard
Which number has exactly 3 factors?
6
8
9
10
Explanation: 9 has factors 1, 3, 9 (a prime squared has exactly 3 factors).
Question 5 of 6
hard
Lights flash every 3 s and 5 s. After how many seconds do they flash together?
8
15
30
10
Explanation: Smallest common multiple of 3 and 5 is 15.
Question 6 of 6
hard
The smallest common multiple of 4, 6 and 8 is…
24
48
12
16
Explanation: 24 is divisible by 4, 6 and 8.