PreAlgebra A ratio is a comparison of two

Pre-Algebra

A ratio is a comparison of two numbers or measures using division. A ratio can be written three ways: 3: 5 3/5 3 to 5 BACK

Ratios are often expressed as fractions in simplest or as a decimal. BACK

A ratio is the comparison of two numbers with the same units by division. A ratio may be written in three ways. What ratios can we form from the tiles above? 12 to 8 BACK

Create as many ratios as possible. Write each ratio three different ways. BACK

Simplest Form • Write the ratio 50 to 300 in simplest form. BACK

Simplest Form • Write the ratio 60¢ per dozen in simplest form. BACK

Look over the ratios you have written. Is there another way that you can write those ratios? The ratio illustrated here is four filled cells to ten total cells. The ratio shown here is two filled cells to five total cells. What do you know about these two ratios? How can you prove your answer? BACK

Unit Rate To find the Unit Rate, you would find the cost or amount for 1. Or the rate when the denominator is 1. “How much for just 1? ” BACK

Unit Rate If it costs $78 for 13 sandwiches, What is the unit rate? BACK

The cost of a 12 -ounce box of Cheerios is $3. 29. Publix brand Cheerios cost $4. 89 for an 18 -ounce box. Find the unit rate to find the better buy. BACK

Mile per Gallon • M. P. G. stands for miles per gallon and is usually used for gas mileage in cars. BACK

Unit Rate • If it takes 11 gallons to drive 250 miles, What is the unit rate or m. p. g. ? BACK

Solving Word Problems • Write problem as proportions: • Solve using cross multiplication. BACK

Unit Price: Price per Item Measure or Count of Items • Allows shoppers to compare the prices of items quickly and easily

Genuardi’s Paper Plates Unit Price = $2 50 plates = $0. 40 per plate Unit Price = $2 For 9 oz. = $0. 22 per oz. Cereal Unit Price = $2 13. 75 oz For 13. 75 oz. = $0. 15 per oz. Coffee

Oranges 4 lb. Bag $2. 99 Unit Price? M & M’s 14 oz. Bag for $2. 69 Unit Price?

Safeway Select Detergent Wisk Laundry Detergent 300 oz. 100 oz. $10. 99 $4. 99 What is the Unit Price?

Dixie plates Hefty plates $2. 49 2 for $4. 00 24 count 50 count (each pkg. ) Unit Price (per plate)?

Cheerios 3 for $6 13. 75 oz. boxes Unit Price (per oz. )? Cheerios 3 for $7. 00 15 oz. boxes Unit Price (per oz. )?

Bounty: 8 rolls $5. 99 Thirsty: 2 rolls $2. 99 Now you want to compare these two brands, which are both on sale. You have determined that you want 8 rolls of paper towels. Which brand will you buy?

Example: Write the original proportion. Use the cross product property. Divide both sides by 6 to isolate the variable, then simplify.

Now you try it! BACK

If the average person lives for 75 years, how long would that be in seconds?

If the average person lives for 75 years, how long would that be in seconds? To solve this problem we need to convert 75 years to seconds. We can do this by breaking the problem down into smaller parts by converting years to days, days to hours, hours to minutes and minutes to seconds. There are 365. 25 days in one year, 24 hours in one day, 60 minutes in 1 hour, and 60 seconds in a minute. Multiply the fractions, and use unit analysis to determine the correct units for the answer.

John constructs a scale model of a building. He says that 3/4 th feet of height on the real building is 1/5 th inches of height on the model. What is the ratio between the height of the model and the height of the building? If the model is 5 inches tall, how tall is the actual building in feet?

What is the ratio between the height of the model and the height of the building? What two pieces of information does the problem give you to write a ratio? For every 3/4 th feet of height on the building… the model has 1/5 th inches of height. Therefore the ratio of the height of the model to the height of the building is… This is called a scale factor.

If the model is 5 inches tall, how tall is the actual building in feet? To find the actual height of the building, use the ratio from the previous step to write a proportion to represent the question above. Use the cross product. Isolate the variable, then simplify. Don’t forget your units.