First, write the statement as a logical statement (with appropriate notation).
A: "No one is absent."
W: "Weather permits"
S: "We will study outside."
Then we have the proposition, symbolically: $$A\rightarrow(W \rightarrow S)$$
Then, since we want to negate the proposition, we work with:
$$\begin{align} \lnot\Big(A\rightarrow(W \rightarrow S)\Big)& \equiv \lnot\Big(\lnot A \lor (\lnot W \lor S)\Big)\tag{$p\rightarrow q \equiv \lnot p \lor q$}\\\ \\\ & \equiv A \land W \land \lnot S\tag{DeMorgan's}\end{align}$$
So the negation of the statement translated back to English gives us:
> "No one is absent and weather is permitting, but (and) we won't study outside."