A shop weighs ten bags of potatoes. The made-up masses in kg, in order, are 2.4, 2.9, 3.1, 3.3…

Step 1. The median. $\dfrac{3.6\ \text{kg} + 3.8\ \text{kg}}{2} = 3.7\ \text{kg}$.

Step 2. The quartiles. Lower half $2.4, 2.9, 3.1, 3.3, 3.6$, so $Q_1 = 3.1$ kg. Upper half $3.8, 4.0, 4.4, 4.9, 5.6$, so $Q_3 = 4.4$ kg.

Step 3. The IQR. $4.4\ \text{kg} - 3.1\ \text{kg} = 1.3\ \text{kg}$.