Seven white balls and three black ball are randomly placed

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Seven white balls and three black ball are randomly placed in a row. The probability that no two black balls are placed adjacently equals ?

1. 1/2
2. 7/15
3. 2/15
4. 1/3

Correct Option: B

n(S) = ¹⁰C₇ = ¹⁰C₃
n(E) = ⁸C₃
∴ P(E) = n(E)/n(S) = 7/15