For an event \(A\) with decimal Back Odds of \(B\) and Lay Odds of \(L\), where \(P(A) = p\) and \(P(\overline{A})=q\).
\[\begin{align} f_{b} = \frac{pB - 1}{B - 1} \end{align}\]
\[\begin{align} f_{l} = 1 - Lp \end{align}\]
e.g. betting $10, on win, rewards $4 plus wager; then \(b = 0.4\) and \(l = 2.5\)
\[\begin{align} b & = B - 1 \\ l & = \frac{1}{L - 1} = \frac{1}{b} \end{align}\]
Where \(W\) is stake + payout of existing bet (e.g. betting $10 on win with $4 wager; then \(W = 14\)).
To hedge a bet with Lay Odds of \(L\), the backers stake, \(X\) is:
\[\begin{align} X = \frac{W}{L} \end{align}\]