Answer:
3.4
Step-by-step explanation:
Standard deviation of a population is defined as:
σ² = ∑(xᵢ − μ)² / n
The standard deviation of a sample is defined as:
s² = ∑(xᵢ − x)² / (n - 1)
It's not clear which one we have, so let's calculate both.
First, we must find the mean.
μ = (5+12+15+10+12+6+8+8) / 8
μ = 9.5
Now we find the squares of the differences:
(5-9.5)² + (12-9.5)² + (15-9.5)² + (10-9.5)² + (12-9.5)² + (6-9.5)² + (8-9.5)² + (8-9.5)²
= 80
Divide by n:
σ² = 80 / 8
σ² = 10
And take the square root:
σ = √10
σ ≈ 3.2
That's not one of the answers, so let's try the standard deviation of a sample instead of a population.
Instead of dividing by n, we'll divide by n-1:
s² = 80 / 7
And take the square root:
s = √(80/7)
s ≈ 3.4
So that must be it.
Answer:
x = 3
Step-by-step explanation:
7/x - 3/(2x) + 7/6 = 9/x
x(7/x - 3/(2x) + 7/6) = x(9x)
x*7/x - 3*x/(2x) + x*7/6 = x*9x
7 - 3/2 + 7x/6 = 9
7x/6 = 9 - 7 + 3/2
7x/6 = 2 + 3/2
7x/6 = 12/6 + 9/6
7x = 12+9
7x = 21
x = 21/7
x = 3
probe:
7/3 - 3/(2*3) + 7/6 = 9/3
14/6 - 3/6 + 7/6 = 3
(14 - 3 + 7) / 6 = 3
18/6 = 3
This should be the correct answer.
C
14²+21²-√49
196+441-7
630
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