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Experimental units can include things like people, animals, or objects.

The explanatory variable is the one that is changed in order to see the effect on the response variable.

The experimental units are the potatoes used in the experiment. The explanatory variables are storage time and time from slicing until cooking. There are six treatments: fresh picked and cooked immediately, fresh picked and cooked after an hour, stored at room temperature and cooked after an hour, stored at room temperature and cooked immediately, stored in refrigerator and cooked immediately and stored in refrigerator and cooked after an hour. The response variables are ratings of colour and flavour.

In part (a), we determine that there were six treatments and thus we should assign $\frac{300}{6}=50$potatoes to each treatment.

Let us assign a unique number between $1and300$to each potato.

Use slips of paper, a random digit table or a calculator to select $50.$

Unique integer between $1and300$. The corresponding $50$potatoes are then assigned to treatment $1.$

Similarly, we will assign $50$unique potatoes to treatment $2,3,4and5$while make sure that no potatoes were already assigned to a previous treatment.

Finally, the remaining $50$potatoes are assigned to treatment$6.$

The statistical benefit of using potatoes from only one supplier is that the sample size will be small and it will not be complex. The time will be saved and it can be give the result quickly. The statistical drawback of using potatoes from only one supplier is that it will give the bias result as it will not represent the whole population. Thus, the result will not be accurate.

Use a randomized block design with regular potatoes in one block and sweet potatoes in another block. Randomly assign the six treatments for each block in the same way done in part (b). Blocking by type of potato ensures that results are not affected by differences potato type.