. 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 is given this voice recognition test. a. Find the probability at least 3 children do not recognize their mother's voice. b. Find the probability all 20 children recognize their mother's voice. c. Let the random variable X denote the number of children who do not recognize their mother's voice. Find the mean of X. d. Let the random variable X denote the number of children who do not recognize their mother's voice. Find the variance of X. e. Find the probability that at most 4 children do not recognize their mother's voice?