An Internet service provider requires its customers to select a password consisting of fourletters followed by three digits. Find how many such passwords are possible in each of thefollowing cases:(a) Repetition of letters and digits is allowed.(b) Repetition of letters and digits is not allowed.
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.
An Internet service provider requires its customers to select a password consisting of four
letters followed by three digits. Find how many such passwords are possible in each of the
following cases:
(a) Repetition of letters and digits is allowed.
(b) Repetition of letters and digits is not allowed.
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