Ten different letters of an alphabet are given. Five-letter words are...
Given information:
- Ten different letters of an alphabet are given.
- Five-letter words are formed from these given letters.
To find:
The number of words which have at least one letter repeated.
Solution:
To find the number of words that have at least one letter repeated, we can use the concept of complementary counting.
Step 1: Find the total number of possible 5-letter words:
Since we have ten different letters, we can choose any one of them for each position in the word. Therefore, the total number of possible 5-letter words is 10^5 = 100,000.
Step 2: Find the number of words with no repeated letters:
For the first letter, we can choose any one of the ten letters.
For the second letter, we can choose any one of the remaining nine letters.
Similarly, for the third, fourth, and fifth letters, we can choose from the remaining eight, seven, and six letters respectively.
Therefore, the number of words with no repeated letters is 10 * 9 * 8 * 7 * 6 = 30,240.
Step 3: Find the number of words with at least one letter repeated:
To find the number of words with at least one letter repeated, we subtract the number of words with no repeated letters from the total number of possible words.
Number of words with at least one letter repeated = Total number of possible words - Number of words with no repeated letters
= 100,000 - 30,240
= 69,760.
Therefore, the number of words that have at least one letter repeated is 69,760.
Ten different letters of an alphabet are given. Five-letter words are...
Number of 5-letter words with at least one letter repeated
= Total number of 5-letter words - Number of 5-letter words with all different letters
= 105 - 10P5
= 69,760
To make sure you are not studying endlessly, EduRev has designed JEE study material, with Structured Courses, Videos, & Test Series. Plus get personalized analysis, doubt solving and improvement plans to achieve a great score in JEE.