Answer:
A. 31/100
Step-by-step explanation:
Change 3/10 to hundreds:
3/10 × 10/10 = 30/100
The denominator (the bottom number) must be 100.
61 - 30 is 31.
The missing number is 31/100. See image.
Complete question is;
An online store receives customer satisfaction ratings between 0 and 100, inclusive. In the first 10 ratings the store received, the average (arithmetic mean) of the ratings was 75. What is the least value the store can receive for the 11th rating and still be able to have an average of at least 85 for the first 20 ratings?
Answer:
50
Step-by-step explanation:
We are told that In the first 10 ratings the store received arithmetic mean of the ratings = 75.
Thus;
Sum of the first 10 ratings = 75 × 10 = 750
Now, for the mean of the first 20 ratings to be at least 85, it means that the sum of the first 20 ratings would be; 85 × 20 = 1700
Thus, the sum of the next 10 ratings would be; 1700 − 750 = 950.
If maximum rating = 100, then the maximum possible value of the sum of the 12th to 20th ratings is given by;
9 × 100 = 900.
Now, in order to make the store have an average of at least 85 for the first 20 ratings, the least value for the 11th rating is;
950 − 900 = 50
The z or t score to be used is (0.422,0.978)
How to find the critical value ?
Critical probability (p*) = 1 - (Alpha / 2), where Alpha is equal to 1 - (the confidence level / 100), is the unit statisticians use to determine the margin of error within a set of data in statistics.
The critical value for α = 0.13 is 
The corresponding confidence interval is computed as shown below
CI = (0.422, 0.978)
0.422< mu1 - mu 2 < 0.978
To learn more about finding the critical value from the given link
brainly.com/question/14040224
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identity used is
x³ + y³+ z³– 3xyz = (x + y + z) (x² + y² + z² – xy – yz – zx).
then use
(x+y+z)² = x²+y²+z²+2(xy+yz+xz)
225= 83 + 2(xy+yz+xz)
xy+yz+xz = (225-83)/2
xy+yz+xz= 142/2
xy+yz+xz= 71
ok
now use identity
x³ + y³+ z³– 3xyz = (x + y + z) (x² + y² + z² – xy – yz – zx).
now
x³ + y³+ z³– 3xyz = 15 (83 – xy – yz – zx).
= 15[83 - (71)]
= 15×12
=180
To what?? Please explain.
