We know the mean of our Bernoulli random variable is going to be the proportion of yellow balls in this population. So it's going to be equal to P, which in this particular case we know is 0.6. And we know what the standard deviation of this Bernoulli random variable is. It is going to be P times one minus P. Actually, that's the variance. We want to take the square root of that to get the standard deviation. So in this particular scenario, that's going to be the square root of 0.6 times 0.4. Fair enough.