Pre Algebra (Period 2 & 4)

Proportions 6-2

A proportion = 2 equal ratios (2 equivalent fractions)

Solve using equivalent fractions or

Cross multiplication and then a one-step equation

(see if you can simplify the fractions before multiplying)

Example: Solve the proportion for y:


4/3 = y
/21

EQUIVALENT FRACTION APPROACH:
Multiply both top and bottom by 7, y = 28



CROSS PRODUCTS APPROACH:

You'll get 3y = (21)(4)
Now divide each side by 3.
Do this before multiplying on the right side!
Why? Because a lot of the time you'll be able to simplify and keep the numbers smaller!


3y/3 = (21)(4) /3

See how the 3 cross cancels into the 21?
so y = 28


ALWAYS SIMPLIFY THE FRACTIONS FIRST!

WORD PROBLEMS WITH PROPORTIONS:


It's all about setting up the LABELS first!


label A _____________ = ____________ label A

label B xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxlabel B