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zorro
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Homework Statement
The probability that a randomly chosen 3 digit number has exactly 3 factors is
1)2/225
2)9/900
3)1/800
4)None of these
The Attempt at a Solution
No idea.
hikaru1221 said:2/ If we exclude 1 and the number itself, then there is no way we can construct such number (Why?).
hikaru1221 said:@jbunniii: 105 is divisible by 3, 5, 7 and 3*5, 3*7, 5*7, so how many factors are there?
P.S.: These are under the assumption that we don't count negative factors. Even if we do, it would be pointless, as there is no number with odd number of factors if negative factors are included.
This is a good analysis. Such things improve your math.hikaru1221 said:EDIT: Rethinking of the question, it's a bit tricky, depending on the way we interpret the question.
1/ If we count 1 and the number itself as its factors, then the only way to construct such number is A = B2 where B is a prime number. Then B should range from 10 to 31. Count the number of possible B's.
2/ If we exclude 1 and the number itself, then there is no way we can construct such number (Why?).
3/ If we exclude 1, then A = BC, where B and C are prime numbers (Why only 2 numbers? Why prime?). However, counting prime numbers up to 999 is a very very tough task
Stephen Tashi said:Abdul,
Where you get these problems that you have posted recently?
berkeman said:Just a friendly reminder to y'all that this is a Homework Help forum, and we are not allowed to do the OP's work for him. Please stick to hints and questions, and ensure that the OP does the bulk of the work. Thanks.
Having exactly 3 factors means that the number can only be evenly divided by 1, itself, and one other number. For example, the number 12 has exactly 3 factors (1, 2, and 6) while the number 13 has more than 3 factors (1 and 13).
The probability of randomly choosing a number with exactly 3 factors is approximately 0.111 or 11.1%. This means that out of every 100 randomly chosen 3-digit numbers, around 11 will have exactly 3 factors.
Yes, there is a pattern. Numbers with exactly 3 factors are always perfect squares, meaning they are the result of multiplying a number by itself. For example, 9 is a perfect square and has exactly 3 factors (1, 3, and 9).
Yes, there are a few exceptions to the pattern. The numbers 1, 4, and 27 also have exactly 3 factors, but they are not perfect squares. These numbers are known as "Carmichael numbers" and are rare occurrences.
The probability of choosing a number with exactly 3 factors decreases as the range of numbers increases. For example, if we extend the range to include all positive integers, the probability becomes 0%. This is because there are infinitely many numbers with more than 3 factors, making the chances of choosing one with exactly 3 factors infinitely small.