Final answer:
To write the error interval for d, we need to consider the uncertainty or error associated with the measurement. In this case, the error interval is 5 km.
Step-by-step explanation:
The distance between two towns, d, is 50 km rounded to 1 significant figure. To write the error interval for d, we need to consider the uncertainty or error associated with the measurement. Since we are rounding to 1 significant figure, the error interval will be half of the unit in the last significant figure. In this case, the unit is 10, so the error interval is 10/2 = 5 km. Therefore, we can write the error interval as
45 km ≤ d ≤ 55 km.