### Instruction: Classify each of the numbers as prime or composite - 1, 2, 3, 10, 15
### Response: Modern mathematicians define a number as prime if it is divided by exactly two numbers. Since 1 can be divided by 1 and the number itself, which is also 1, so 1 is a prime number. By the same definition 2 and 3 are also prime numbers. Whereas, 10 and 15 are composite numbers as they can be divided by 4 numbers each. 10 can be divided by 1, 2, 5 and 10. 15 can be divided by 1, 3, 5 and 15.