A proportion looks like this:

It means that the quantity a,b,c and d are in the same proportion: the ratio between a and b is the same ratio between c and d.
They are particularly useful in situation when you have an example given, and you want to extrapolate the relationship for another couple.
For example, you can think of the following problem: "Five apples cost 2 dollars. How much will 8 apples cost?"
You can build the proportion

And then solve it for x:

Answer:
1.
÷
---> 
2.
---> 
3.
---> 
4.
--> 
Step-by-step explanation:
Given that:
1. 

Thus,
÷
=
÷ 
Flip the 2nd function, Q(x), upside down to change the process to multiplication.



2.
= 
Make both expressions as a single fraction by finding, the common denominator, divide the common denominator by each denominator, and then multiply by the numerator. You'd have the following below:





3.
= 





4. 


Answer:
$482.625 ≈ $482.63
Step-by-step explanation:

y · 100 = 450 · 7.25
100y = 3262.5
100y ÷ 100 = 3262.5 ÷ 100
y = 32.625
$450 + $32.625
$482.625
Answer:
x-9
Step-by-step explanation:
"Less than" switches the way of the expression.
If the "less than" was not there it would have been:
9-x
"Less" means subtract so you would subtract x from 9.
Hope this helped!
Answer:
The traveler can plan such a tour in 3003 ways.
Step-by-step explanation:
The order that the cities are chosen is not important, since it is chosen by the company and not by the traveler. So we use the combinations formula to solve this question.
Combinations formula:
is the number of different combinations of x objects from a set of n elements, given by the following formula.

In this problem, we have that:
Combinations of 5 cities from a set of 15. So

The traveler can plan such a tour in 3003 ways.