Answer:
1 to 50 is the possible random picks, and there are 50 of those. The prime ones are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47,. So there are 15 primes in that range. If every number has the same chance of being drawn then the odds are 15 out of 50, which can be reduced to 3 out of 10 or 30%
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Total out comes n(s)=50
Favorable outcomes A={2,3,5,7,11,13,17,19,23,29,31,37,41,43,47}
n(A)=15
p(A)=15/50=3/10