AnswersNC-Math 4 CRObservational Studies and ExperimentsQuestion 9
9
AssignmentMultiple Choice

Observational Studies and Experiments

Question 9 • NC-Math 4 CR

A company wants to test clear deck sealants for weather resistance. Three brands of sealants will be tested using nine pieces of decking wood. The company wants to randomly assign the pieces of wood to the treatment groups using a table of random digits to produce three equal-sized groups suitable for comparison. Select the appropriate design.

Answer
A
Select a piece of wood from the pile, and then, reading from left to right on a random number table, identify the first digit. If the first digit is 1, 2, or 3, assign the wood to sealant 1. If the first digit is 4, 5, or 6, assign it to sealant 2. If the first digit is 7, 8, or 9, assign it to sealant 3. Continue with the second piece of wood and the second digit in the table, and so on.
B
Number each piece of wood with a digit from 1–9. Read from left to right, looking at one digit at a time on a random number table to identify 9 unique one-digit numbers from 1–9. Assign the wood labeled with the first 3 numbers to sealant 1, the wood labeled with the next 3 numbers to sealant 2, and the remaining wood to sealant 3.
C
Randomly number each piece of wood with 1, 2, or 3. Assign the wood labeled 1 to sealant 1, the wood labeled 2 to sealant 2, and the wood labeled 3 to sealant 3.
D
Use the first 9 digits reading from left to right on a random number table to assign a number to each piece of wood. Then, wood that is labeled with a 0, 1, 2, or 3 is assigned to sealant 1, wood labeled with a 4, 5, or 6 is assigned to sealant 2, and wood labeled with a 7, 8, or 9 is assigned to sealant 3.

Explanation

Number the nine pieces of wood 1 through 9, then use the random-digit table to select a random order of all nine numbers without repeats. Assign the first three pieces in that order to sealant 1, the next three to sealant 2, and the last three to sealant 3. This gives each sealant exactly three pieces while making the assignments random; the other methods do not guarantee equal-sized groups.

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