Find the number which is NOT a prime number.

Options

A. 89
B. 87
C. 79
D. 97

Answer

To find the number which is NOT a prime number from the given options (89, 87, 79, and 97), we will analyze each number to determine if it is prime or composite.

### Step-by-Step Solution:

1. **Understand what a prime number is**: A prime number is a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers. In other words, a prime number has exactly two distinct positive divisors: 1 and itself.

2. **Check each option**:
- **Option 1: 89**
- The factors of 89 are 1 and 89.
- Since it has only two factors, 89 is a prime number.

- **Option 2: 87**
- The factors of 87 are 1, 3, 29, and 87.
- Since it has more than two factors, 87 is NOT a prime number (it is a composite number).

- **Option 3: 79**
- The factors of 79 are 1 and 79.
- Since it has only two factors, 79 is a prime number.

- **Option 4: 97**
- The factors of 97 are 1 and 97.
- Since it has only two factors, 97 is a prime number.

3. **Conclusion**: Among the options provided, the only number that is NOT a prime number is **87**.

### Final Answer:
The number which is NOT a prime number is **87**.