Answer:
In order to solve this problem, The Rule of Three, will be helpful. This rule is useful in this case in which we are working with proportions or quantities and we have three given values and we need to find the fourth value.
This is how it works:
If we have three given quantities A, B and C, in which A is equivalent to B and C is equivalent to D (the unknown quantity), we can expressed it as follows:
A----B
C----D
Or
[tex]D=\frac{(C)(B)}{A}[/tex]
For this problem:
8 apples cost $4
9 apples cost $?
Or
8 apples----$4
9 apples----$?
Then:
[tex]\$?=\frac{(9apples)(\$4)}{8apples}[/tex]
$?=$4.5
Finally the answer is: 9 apples cost $4.5
