How many 4-digit numbers are there if no digit is repeated?
Or
How many numbers are there between 1000 and 9999 so that no digit is repeated?
How many words, with or without meaning, can be formed using all the letters of the word EQUATION at a time so that the vowels and consonants occur together?
Number of letters = (all distinct)
Number of vowels = 5 (e, i, o, u, a)
Number of consonants = 3 (q, t, n)
Step I: Tie the vowels together
Number of permutations =
Step II: Tie the consonants together.
Number of permutations =
Step III: Mix the bundles and any remaining letter to give 1 + 1 + 0 = 2 letters.
Number of permutations =
Hence, the number of permutations, using, fundamental principle of counting
= 120 x 6 x 2 = 1440
How many words, with or without meaning, can be formed using all the letters of the word EQUATION at a time so that no two consonants are together.