I am a common factor of 20 and 60. I am a multiple of 4 and 10. I am greater than 9. What number am I?
Factors of 20: 1, 2, 4, 5, 10, 20
Factors of 60: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60
Highest common factor of 20 and 60: 20
Multiples of 4: 4, 8, 12, 16, 20
Multiples of 10: 10, 20
Lowest common multiple of 4 and 10: 20
The number is 20.
Answer(s): 20