Answer:
Swap 10 from box A and 15 from box B
Step-by-step explanation:
For calculate the ratio between the boxes we find the mean of the box A and the mean of the box B and divide this two results.
For find the mean of a set you use the next formula [tex]\bar{x} = \frac{\text{sum numbers}}{\text{total numbers}}[/tex]
[tex]\bar{A} = \frac{4+5+9+10+12}{5} = \frac{40}{5}= 8\\\bar{B} = \frac{6+7+13+15+19}{5} = \frac{60}{5}= 12[/tex]
Then the ratio is equal to [tex]\frac{\bar{A}}{\bar{B}} = \frac{8}{12} = \frac{2}{3}[/tex]
Know the ask us for a ratio of 9:11 then we know two things about the boxes.
If you swap the numbers between them the total of numbers in the mean not change is always 5 and the sum of all the elements in both boxes is always 100. With this we can state the next equation:
The new mean of [tex]\bar{A}[/tex] is 9 then:
[tex]\frac{\text{sum of elements in box A}}{5} = 9[/tex]
[tex]\text{sum of elements in box A} = 45[/tex]
The new mean of [tex]\bar{B}[/tex] is 11 then:
[tex]\frac{\text{sum of elements in box B}}{5} = 11[/tex]
[tex]\text{sum of elements in box B} = 55[/tex]
Now we know what is the sum of the elements in both boxes, but how we find the elements for swap? Well with the next relation.
When you take out a element from the box A this elements is substracted to the total sum of the elements in the box A and get a new sum of total of elements named [tex]c[/tex] (where [tex]a[/tex] is the element taken):
[tex]40 - a = c[/tex]
And when you sum an element to the box A the current sum of total elements in the box change to (where [tex]b[/tex] is the added element):
[tex]b + c = 45[/tex]
So replace [tex]c[/tex] for the first relation and get:
[tex]b + 40 - a = 45\\b - a = 5[/tex]
From the last equation you can deduct that [tex]b[/tex] is greater than [tex]a[/tex] and the different between both values is 5. So the last step is find a number in the box B that substracted to a number from the box A give us 5. These both numbers are 15 and 10 because 15 - 10 = 5.
