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I following Susanna Epps book for discrete math & I am not able to solve the following :

In another state, all license plates consist of from four to six symbols chosen from the 26 letters of the alphabet together with the ten digits 0-9.

a. How many license plates are possible if repetition of symbols is allowed?

b. How many license plates do not contain any repeated symbol?

c. How many license plates have at least one repeated symbol?

Only answer for C is given.

a. $36^4+36^5+36^6$

b. $^{36}P_4+^{36}P_5+^{36}P_6$

c. $ans(a)-ans(b) = 789865128$

but answer in book given as 774,372,096. What I am getting wrong ? Any subtle hint will do.

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    $\begingroup$ Your answer is what I get. $\endgroup$ – Brian M. Scott Apr 7 '13 at 4:33
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You're correct; the answer given by the book is incorrect (it happens sometimes).

Here is the entry in the official errata for the book (A-79 – 9.3 #7)

| cite | improve this answer | |
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  • $\begingroup$ Oh, thank you ! that's quite a relief. $\endgroup$ – avi Apr 7 '13 at 4:38

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