A letter lock consists of 4 rings, each ring contains 9 non-zero digits. This lock can be opened by setting four digit code with the proper combination of each of the 4 rings. Maximum how many codes can be formed to open the lock ? Select the correct option.
A) 4(9) B) 9(4) C) 9P4 D) None of these E) Cannot be determined
Solution: There are 9 non-zero digits to arrange themselves at 4 different position. Each letter can be arrange at different position in 9 different ways.   So, required number of ways,   = 9 *9 *9 *9   = 94.   Answer: Option 9(4)
<result>B</result>
A letter lock consists of 4 rings, each ring contains 9 non-zero digits. This lock can be opened by setting four digit code with the proper combination of each of the 4 rings. Maximum how many codes can be formed to open the lock ?