From Past Experience, It Is Known 90% of One-Year-Old Children

From past experience, it is known 90% of one-year-old children can distinguish their mother's voice from the voice of a similar sounding female. A random sample of 20 one-year-olds are given this voice recognition test.
Find the probability at least 3 children do not recognize their mother's voice.
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Find the probability all 20 children recognize their mother's voice.
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Let the random variable x denote the number of children who do not recognize their mother's voice. Find the mean of x.
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Let the random variable x denote the number of children who do not recognize their mother's voice. Find the variance of x.
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Find the probability that at most 4 children do not recognize their mother's voice.
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