Is it 1321/2187?

P(atleast 2 primes) = 1 - {P(no primes) + P(exactly 1 prime)}

Primes = 2,3,5,7

Non-primes = 1,4,6,8,9

P{no primes} = 5*5*5*5/9^4

P{exactly 1 prime} = (4*5*5*5/9^4)*4C1 [ The given prime can occupy any 1 of the 4 places]

P(atleast 2 primes) = 1 - {625+2000}/9^4 = 1321/2187

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