Description:
Ratio problems ask you to compare quantities of various items and answer
questions about them.
Approach:
Most ratio questions can be easily solved if you create a chart
with the quantities you know and the quantities you want to find.
1) Find the Missing Number
When a ratio question provides a ratio of two quantities, it is often
helpful to add the two quantities.
For example, if the ratio of cars to
trucks in a parking lot is 3:5 then the "missing number" is 8.
If the
problem said that there were 40 cars and trucks total in the parking lot,
then you create a proportion with 40 and 8.
This proportion can then be
used to solve for the number of cars or trucks in the parking lot.
40 ⁄ 8 = Cars ⁄ 3 = Trucks ⁄ 5
1-1. Practice:
The ratio of goldfish to beta fish in Bobby's aquarium is 3 to 2.
If Bobby
has a total of 45 fish, how many fish are betas?
-
12
-
15
-
18
-
21
-
24
2) Ratio:Ratio:Ratio
Ratio parts don't always reference the same whole.
Consequently, make
sure the common portion of both ratios is the same quantity.
For example:
In Billy's marble collection the ratio of red to blue
marbles is 5:2.
The ratio of blue marbles to yellow marbles is 3:4.
What is the ratio of red to yellow marbles?
The answer is not 5:4.
-
Change the two ratios so that the blue quantity is the same in both:
R:B = 15:6 and B:Y = 6:8
-
Now that blue is the same (6) in both ratios, the ratio of R:Y can be
calculated to be:
15:8
2-1. Practice:
If the ratio of cats to dogs is 3:5 and the ratio
of dogs to people is 6:7, what is the ratio of cats to people?
-
3:7
-
1:2
-
18:35
-
6:7
-
7:5
