The number of two digit numbers which are prime :

Options

A. 25
B. 23
C. 21
D. can't be determined

Answer

To find the number of two-digit prime numbers, we can follow these steps:

### Step 1: Identify the range of two-digit numbers
Two-digit numbers range from 10 to 99.

### Step 2: Understand what a prime number is
A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself.

### Step 3: List all prime numbers from 1 to 100
The prime numbers between 1 and 100 are:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.

### Step 4: Count the total prime numbers from 1 to 100
From the list above, we can see that there are a total of 25 prime numbers between 1 and 100.

### Step 5: Identify and count the one-digit prime numbers
The one-digit prime numbers are:
2, 3, 5, 7.
There are 4 one-digit prime numbers.

### Step 6: Calculate the number of two-digit prime numbers
To find the number of two-digit prime numbers, we subtract the number of one-digit prime numbers from the total number of prime numbers:
Total prime numbers (25) - One-digit prime numbers (4) = Two-digit prime numbers.

So, we have:
25 - 4 = 21.

### Conclusion
The total number of two-digit prime numbers is 21.

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