Answer:
The diameter of the potatoes used is 6 cm ⇒ answer D
Step-by-step explanation:
* Lets explain how to find the median of same data
- At first you must arrange the data
- Divide the number of data by 2 to find the middle one
- If the number of the data is odd, then we have one middle number
# Ex: if the number of the data is 5 then the middle one is the
 third number
- If the number of the data is even, then we have two middle numbers,
 so we take their average
# Ex: If the number of the data is 6 then the third and the fourth
 are the middle numbers, then the median will be half their sum
* Now lets solve the problem
∵ The data are 3 , 3 , 4 , 4 , 5 , 6 , 7 , 8 , 9
- There are 9 numbers
∴ The fifth number is the middle number
∴ The median = 5
- Kristin used one of them
∴ The number of the data is now 8
∵ The median is the average of the middle two numbers x1 , x2
∴ The median = (x1 + x2)/2
∵ The value of the median 4.5
∴ 4.5 = (x1 + x2)/2 ⇒ multiply both sides by 2
∴ x1 + x2 = 9
∴ The two middle numbers are 4 and 5 because their sum = 9
- We have three numbers before the middle term
- We have four number after the middle term
∴ We can take out 6 or 7 or 8 or 9
∵ The answer has only 6
∴ The diameter of the potatoes used is 6 cm
