A proportion is a statement of equality of two or more ratios Remember: A ratio is a comparison of two numbers by division

A proportion is a statement of equality of two or more ratios

Remember: A ratio is a comparison of two numbers by division

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Find the two things you are comparing!!

First Step:

Suppose it takes 48 chicken fingers to feed Mr. Young’s 4th grade class of 20 students. How many chicken fingers would be needed for 30 students?

And the answer is…….Chicken Fingers and Students

Chicken Fingers Students---------------------- OR -------------Students Chicken Fingers

As a Ratio this looks like…..


Jane ran 100 meters in 15 seconds. How long did she take to run 1 meter?

And the Answer is….Meters and Seconds

Meters Seconds---------- OR ------------Seconds Meters


A car travels 125 miles in 3 hours. How far would it travel in 5 hours?

And the answer is….Miles and Hours


Miles Hours--------- OR --------Hours Miles

Make the two ratios (fractions) that you know

Second Step:


First Step:Chicken Fingers Students---------------------- OR --------------Students Chicken Fingers


And the answer is….

Chicken Fingers 48 X-------------------- ------ AND ----- Students 20 30

FYI Can you flip the ratio so that students

were on top and chicken fingers were on bottom?

YES! If you flip the ratios so that students are on top and chicken fingers were on bottom you must just be careful to do this for all your ratios. Therefore then 48/20 would change to 20/48 and

x/30 would become 30/x.

Chicken Fingers 48 X-------------------- ---- AND ----Students 20 30

OR Students 20

30----------- ------ AND ------- Chicken Fingers 48 X


Meters Seconds---------- OR ------------Seconds Meters

First Step:


And the answer is…..Meters 100 1--------- ------ AND -------Seconds 15 X


And the answer is…..

Miles 125 X------- ------ AND -------Hours 3 5

Third Step:Set the two ratios EQUAL to each other

1. Chicken Fingers ----------------------

Students

2. 48 X---- AND ----20 30

3. 48 X ----- = --- 20 30



And the answer is……

1. Meters ---------- Seconds

2. Meters 100 1--------- ------ AND -------Seconds 15 X

3. 100 1 ------ = ------- 15 X


And the answer is…..

1. Miles ------- Hours2. Miles 125 X ------- ------ AND

------- Hours 3 52

3. 125 X ------ = ------- 3 5

Fourth Step:Cross Multiply

Cross Multiply means that you MULTIPLY DIAGONALLY across…..

…….Like crisscross apple sauce when you are sitting

And then…..Set the two products (ANSWERS) EQUAL to each

other

4X = 63

Fifth Step:Solve for X!!!

48 X ----- = --- 20 30

And the answer is….

30 students would eat 72 chicken fingers

100 1 ------ = ------- 15 X

And the answer is…(100)(X)= (15)(1)100X= 15X= 15/100X= .15 It took Jane .15 seconds to run a meter

100 1 ------ = ------- 15 X

125 X ------ = ------- 3 5

(125)(5) = (3)(X)625 = 3X625/3=XX= 208.3In 5 hours the car would have traveled 208.3

miles.

125 X ------ = ------- 3 5

Mix 3 liters of water with 4 lemons to make lemonade. How many liters of water are mixed with 8 lemons.

1. What are you comparing?Liters and LemonsLiters Lemons------- OR -------Lemons Liters


2. What are your two ratios? Liters 3 X --------- ------ AND ------

Lemons 4 8

3. Set the two ratios equal to each other 3 X ---- = -----

4 8



4. Cross Multiply 3 X---- = ----- (4)(X) = (3)(8) 4 8

5. Solve4X= 24X= 24/4X= 6You will need 6 liters of water for 8 lemons.

3 gallons of paint cover 900 square feet. How many gallons will cover 300 square feet?

The answer is 1 gallon of paint for 300 square feet.

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A proportion is a statement of equality of two or more ratios Remember: A ratio is a comparison of two numbers by division