Question 1200602
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The total possible number of described passwords is  10*9*8*7,

based on commonly known logic (the product of 4 integer numbers in descending order, starting from 10).



Of them, the number of the passwords that started from 7, is  9*8*7,

since one of the digit, 7, is just nailed to the first position.



Therefore, the probability under the problem's question is  {{{(9*8*7)/(10*9*8*7)}}} = {{{1/10}}} = 0.1 = 10%.    <U>ANSWER</U>
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Solved.