Let $X$ be a Poisson random variable with mean $\mu$, representing the number of errors on a page of this book. Each error is independently a grammatical error
119 with probability $p$ and a spelling error with probability $1-p$. If $Y$ and $Z$ are random variables representing the number of grammatical and spelling errors (respectively) on a page of this book, prove that $Y$ and $Z$ are Poisson random variables with means $\mu p$ and $\mu(1-p)$, respectively. Also, prove that $Y$ and $Z$ are independent.