Each employee at a large company is to be issued an ID number; the ID number is to consist of one letter, followed by three digits (0 to 9), and followed by another letter. How many ID numbers are possible if the repetition is allowed? How many ID numbers are possible if letters cannot repeat and the first digit cannot be an odd number?
Permutations and Combinations
If there are 5 dishes, they can be relished in any order at a time. In permutation, it should be in a particular order. In combination, the order does not matter. Take 3 letters a, b, and c. The possible ways of pairing any two letters are ab, bc, ac, ba, cb and ca. It is in a particular order. So, this can be called the permutation of a, b, and c. But if the order does not matter then ab is the same as ba. Similarly, bc is the same as cb and ac is the same as ca. Here the list has ab, bc, and ac alone. This can be called the combination of a, b, and c.
Counting Theory
The fundamental counting principle is a rule that is used to count the total number of possible outcomes in a given situation.
Each employee at a large company is to be issued an ID number; the ID number is to consist of one letter, followed by three digits (0 to 9), and followed by another letter.
- How many ID numbers are possible if the repetition is allowed?
- How many ID numbers are possible if letters cannot repeat and the first digit cannot be an odd number?
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