how many different digit number are there which have digit 1,2,3,4,5,6,7,8, such that digit 1 appears exactly once ?  Choices.
A) 4C1 * 7^2
B) 4C1 * 7^3
C) 4C1 * 7^4
D) 4C1 * 7^5
E) 4C1 * 7^6
Digit 1 can appear in any of the 4 positions of a 4 digit number =&gt; 4C1   Further,as repetition is allowed,the othe three digits can have any of the remaining 7 numbers   So total no of different 4 digit numbers possible = 4C1 * 7 * 7 *7 = 4C1 * 7^3   ANSWER:4C1 * 7^3
<result>B</result>
how many different digit number are there which have digit 1,2,3,4,5,6,7,8, such that digit 1 appears exactly once ?