Answer:
Option C is correct.
Step-by-step explanation:
We have been given total 8 data
Data is : 12,15,18,20,23,23,28
Here, n=7
Median is 
Median is 20.
When one data is added n=8
The median of even number of data is

Median is
Median is 
4th terms is 20
5th terms is 23
Since, median should not be change hence,
Median will be 20.
Therefore, option C is correct.
There are 12 boys enrolled in algebra 2
Answer:
x : y = 9 : 13
Step-by-step explanation:
Given that
3x - y : x + 2y = 2 : 5
Express the ratio in fractional form, that is
=
( cross- multiply )
5(3x - y) = 2(x + 2y) ← distribute parenthesis on both sides )
15x - 5y = 2x + 4y ( subtract 2x from both sides )
13x - 5y = 4y ( add 5y to both sides )
13x = 9y ( divide both sides by 13 )
x =
y ( divide both sides by y )
=
, that is
x : y = 9 : 13
Y=2x+320
x being the number of years and 320 being the initial population of mice