First, conceptually understand what an inverse function is, it makes solving it very intuitive. An inverse function is simply a function which has points (y,x) for every point (x,y) of the parent function. So you are essentially taking all points of the parent function and switching the x and y coordinates for each. Those switched coordinates are produced by the "inverse function".
Mathematically then, finding the inverse function is a matter of solving for x and then switching the variable labels. In this case:
y=2x+1 subtract 1 from both sides
y-1=2x divide both sides by 2
(y-1)/2=x now just switch the labels for the variables...
y=(x-1)/2 so
f^-1(x)=(x-1)/2 is the inverse of f(x)=2x+1
Let us formulate the independent equation that represents the problem. We let x be the cost for adult tickets and y be the cost for children tickets. All of the sales should equal to $20. Since each adult costs $4 and each child costs $2, the equation should be
4x + 2y = 20
There are two unknown but only one independent equation. We cannot solve an exact solution for this. One way to solve this is to state all the possibilities. Let's start by assigning values of x. The least value of x possible is 0. This is when no adults but only children bought the tickets.
When x=0,
4(0) + 2y = 20
y = 10
When x=1,
4(1) + 2y = 20
y = 8
When x=2,
4(2) + 2y = 20
y = 6
When x=3,
4(3) + 2y= 20
y = 4
When x = 4,
4(4) + 2y = 20
y = 2
When x = 5,
4(5) + 2y = 20
y = 0
When x = 6,
4(6) + 2y = 20
y = -2
A negative value for y is impossible. Therefore, the list of possible combination ends at x =5. To summarize, the combinations of adults and children tickets sold is tabulated below:
Number of adult tickets Number of children tickets
0 10
1 8
2 6
3 4
4 2
5 0
