How many 3-digit numbers can be formed with the digits 1,4,7,8 and 9 if the digits are not repeated?

Sure, here is the step by step solution:

Step 1: Identify the number of digits to be used. In this case, we are forming 3-digit numbers.

Step 2: Identify the number of available unique digits. Here, we have 5 unique digits (1,4,7,8,9).

Step 3: Use the concept of permutations since the order of digits matters in a number.

Step 4: The number of ways to choose the first digit is 5 (any of the 5 digits).

Step 5: Once the first digit is chosen, we are left with 4 digits. So, the number of ways to choose the second digit is 4.

Step 6: Similarly, the number of ways to choose the third digit is 3 (since two digits have already been used).

Step 7: Multiply these values together to get the total number of 3-digit numbers.

So, the total number of 3-digit numbers that can be formed is 543 = 60.