Answer
$rate=-\frac{(\Delta B)}{\Delta t}=(\frac{1}{2})(\frac{\Delta A}{\Delta t})$
Work Step by Step
Rate of reaction is a function of the change in reactant or product over time. Since B is decreasing and rate must be positive, the sign must be reversed. Since 2 units of A are produced in each reaction, the change in concentration must be halved to find the rate.
