The 25th percentile corresponds to z ≈ -0.67.
The 90th percentile corresponds to z ≈ 1.28.
So, you can write two equations in μ and σ as here:
.. μ -0.67σ = 10
.. μ +1.28σ = 20
The solution is
.. μ ≈ 13.45
.. σ ≈ 5.11
It is related to econometrics, however using simple algebraic logic we can solve this problem. General formula with residual is

, where r is a residual. Plugging the pair into the formula, we obtain that

and r=0.5
I don’t know the answer to this bc I can’t remember
Its the last one because both have divisions of the same thing and don't worry I checked it twice
4/20 = 1/5
9/24 = 3/8
18/30 = 3/5
9/12 = 3/4
9/21 = 3/7
5/45 = 1/9
20/25 = 4/5
10/12 = 5/6
6/9 = 2/3
4/40 = 1/10
Explanation:
Find the greatest common factor then divide the numerator and denominator by the greatest common factor
Hope This Helps :)