Prime number

Jan wrote any number from 1 to 20. What is the probability that he wrote the prime number?

Result

p =  0.4

Solution:

p:2;3;5;7;11;13;17;19  p=820=25=0.4p: 2; 3; 5; 7; 11; 13; 17; 19 \ \\ \ \\ p=\dfrac{ 8 }{ 20 }=\dfrac{ 2 }{ 5 }=0.4

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