Question 1207742
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Serial numbers for a product are to be made using 4 letters followed by 4 digits. 
The letters are to be taken from the first 7 letters of the alphabet, with no repeats. 
The digits are taken from the 10 digits (0,1,2, ..., 9), with no repeats. 
How many serial numbers can be generated?
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For first 4 positions, the number of possible 4-letter parts is  7*6*5*4 = 840
(the product of 4 sequential integer numbers in descending order, starting with 7). 


For last 4 positions, the number of possible 4-digit parts is  10*9*8*7 = 5040
(the product of 4 sequential integer numbers in descending order, starting with 10). 


The total number of all possible serial codes is the product  840*5040 = 4233600.    <U>ANSWER</U>
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Solved.