Solution
= Solution
Summing part i and reindexing gives
$$
\boxed{\mathbb P(M_n\geq m)=\mathbb P(X_n=m)+2\sum_{x>m}\mathbb P(X_n=x).}
$$
Subtracting the formula for $m+1$ yields
$$
\boxed{\mathbb P(M_n=m)=\mathbb P(X_n=m)+\mathbb P(X_n=m+1).}
$$
= Solution
Summing part i and reindexing gives
$$
\boxed{\mathbb P(M_n\geq m)=\mathbb P(X_n=m)+2\sum_{x>m}\mathbb P(X_n=x).}
$$
Subtracting the formula for $m+1$ yields
$$
\boxed{\mathbb P(M_n=m)=\mathbb P(X_n=m)+\mathbb P(X_n=m+1).}
$$