Posted by **Mackenzie** on Tuesday, February 26, 2008 at 3:55pm.

your social security number is a 9 digit number. suppose that the last 4 digits are chosen randomly from the number 0-9.

a. how many sequences are possible for the last 4 digits?

b. what is the probability of getting 5 or 0 in the last digit.

c. what is the probability of getting two 5's in the last two digits?

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**drwls**, Tuesday, February 26, 2008 at 5:44pm
a.) 0000 through 9999 = 10,000 possibilities

b.) 1/10 + 1/10 = 1/5

c.) 1 (55) out of 100 (00 through 99)

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**Mackenzie**, Tuesday, February 26, 2008 at 7:30pm
for a i thought you were supposed to do 9*8*7*6 and the answer that i got was 3,024.

for b i got 9*8=72

for c i got 9*9=81

does that make sense

- math -
**PsyDAG**, Wednesday, February 27, 2008 at 11:12am
The numerals get smaller if you are considering probabilities *without replacement*. In other words, using a numeral in one position would prohibit its use in other positions. However, the use of any numeral does not effect the probabilities of the remaining numerals.

I hope this helps a little more. Thanks for asking.

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