How many strings of five ASCII characters contain the character @ (“at” sign) atleast once? Note: There are 128 different ASCII characters

To solve this problem, we can use the principle of inclusion-exclusion.

Step 1: Calculate the total number of strings of five ASCII characters. Since there are 128 different ASCII characters, and each character in the string can be any of these 128 characters, the total number of such strings is 128^5.

Step 2: Calculate the number of strings of five ASCII characters that do not contain the character @. Since there are 127 ASCII characters other than @, the number of such strings is 127^5.

Step 3: Subtract the number of strings that do not contain @ from the total number of strings. This gives the number of strings that contain @ at least once.

So, the answer is 128^5 - 127^5.