2015 AMC 10B Problems/Problem 11
Problem
Among the positive integers less than , each of whose digits is a prime number, one is selected at random. What is the probability that the selected number is prime?
Solution
The one digit prime numbers are , , , and . So there are a total of ways to choose a two digit number with both digits as primes and ways to choose a one digit prime, for a total of ways. Out of these , , , , , , , and are prime. Thus the probability is .
Solution 2
We count the number of primes. We get 25 primes. The only answer choice that has a denominator of 25 (or simplified) is B.
Video Solution
~savannahsolver
See Also
2015 AMC 10B (Problems • Answer Key • Resources) | ||
Preceded by Problem 10 |
Followed by Problem 12 | |
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