Simplify: $\left(\dfrac{1}{3}-\dfrac{1}{4}\right) \div \left(\dfrac{1}{3}+\dfrac{1}{4}\right) \times 7$

$\frac{1}{3}-\frac{1}{4}=\frac{1}{12}$ and $\frac{1}{3}+\frac{1}{4}=\frac{7}{12}$. Dividing gives $\frac{1}{12} \div \frac{7}{12} = \frac{1}{7}$, and multiplying by $7$ gives $1$.