math help. Algebra

Question

1.The fuel for a chain saw is a mix of oil and gasoline. The ratio of ounces of oil to gallons of gasoline is 4:12. There are 24 gallons of gasoline. How many ounces of oil are there?

 

 

2. An architect built a scale model of a shopping mall. On the model, a circular fountain is 15 inches tall and 7.5 inches in diameter. If the actual fountain is to be 10 feet tall, what is its diameter? 

 

Answer 1

Hi Lindsey,

 

A ratio means that you are comparing one number to another.  It's generally written as a fraction. So the ratio of 4 to 12 can be written as 4/12.  Remember that in this ratio, ounces are on the top and gallons are on the bottom.

 

Now set this ratio equal to a new ratio with different gallons on the bottom (24) and unknown ounces on the top:

 

4/12 = X/24

 

Now you can see that the gallons have doubled from 12 to 24.  In order to keep the ratios equal, you will have to double the ounces from 4 to 8.

 

Another way to solve is to cross multiply the two fractions where you multiply the top of the first fraction with the bottom of the other and set that equal to multiplying the bottom of the first fraction to the top of the other:

 

4 x 24 = 12X

 

96 = 12X

 

8 = X

 

Now you should be able to answer question 2.

 

Dan