Assume that 4 digits are selected at random from the set { 1, 2, 4, 6, 7, 9 } and are arranged in random order.What is the probability that the resulting 4-digit number is less than 7000? I’m lost on this type of problem too!

September 11, 2012

Anonymous asked: Assume that 4 digits are selected at random from the set { 1, 2, 4, 6, 7, 9 } and are arranged in random order.What is the probability that the resulting 4-digit number is less than 7000? I'm lost on this type of problem too!

6P4 - 2*5P3 = 240 240/360

6p4 is permutation of selecting a 4 digit number from these six digits

a number is less than 7000 if it does not starts with 7 and 9

so subtract those cases 5p3 is permutations of selecting a four digit number when you have already a number fixed, multiply by 2 to get for both 7 and 9

sample space is 360

so your answer is 240/360

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