Question

12. Find the number of 4 letter words that can be formed using the letters of the word CHEMISTRY.How
many of them begin with the letter C ? How many end with the letter Y. How many begin with Ca
end with Y.​

Answer 1

Answer:

ANSWER

Case 1: If all four letters are different then the number of words =

5

C

4

×4!=120

Case 2: If 2 letters are R and other 2 different letters are chosen from B, A, C, K then the number of words =

4

C

2

×

2!

4!

=72

Case 3: If 2 letters are A and other 2 different letters are chosen from B,R,C,K then the number of words =

4

C

2

×

2!

4!

=72

Case 4: when word is formed using 2R

′

s and 2A

′

s=

2!2!

4!

=6

Then the number of four-letter words that can be formed=120+72+72+6=270

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