The random variable x represents the number of credit cards that adults have along with the corresponding probabilities. find the mean and standard deviation. x p(x) 0 0.07 1 0.68 2 0.21 3 0.03 4 0.01a.mean: 1.23; standard deviation: 0.44b.mean: 1.30; standard deviation: 0.32c.mean: 1.30; standard deviation: 0.44d.mean: 1.23; standard deviation: 0.66