Question 1099807
A credit card number has 16 digits between 0 and 9 inclusive.If only 100 million numbers are valid, what is the probability that a number that is entered ramdomly is valid? 
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Assuming leading zeroes are allowed, ie, 0000000000000001 is used:
1e8/1e16 = 1e-8
--> 0.00000001
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If leading zeroes not allowed:
--> 1e8/9e15
= 1/(9e7)