Solution :
Given that, for binomial distribution mean, np = 4 and variance, npq = 2.
\(\therefore\) q = 1/2, but p + q = 1 \(\implies\) p = 1/2
and n \(\times\) \(1\over 2\) = 4 \(\implies\) n = 8
We know that, P(X = r) = \(^nC_r p^r q^{n-r}\)
\(\therefore\) P(X = 1) = \(^8C_1\)\(({1\over 2})^7\)\(({1\over 2})^1\)
= 1/32
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