PowerPoint Presentation

4-3 Equivalent Ratios and Proportions:4-3 Classwork:

WORKBOOK, page 175

Problems 7 through 12

You have 20 minutes to complete.4-4Solving Proportions 1 2__=__ 2 4

2*2=41*4=4

1 x____=____ 2 4

2x = 4x=2Remember how we solved ratios to see if they were proportionate?

Cross multiplying is always the best choice:

If a value is missing, we still do the same thing, cross multiply and solve for the missing amount:

Divide both sides by 2

Now take the amount you solved and put it in place of the x:1x122424

Lets Practice 6=36 ____ 10 x

Cross Multiply

6 * x = 6x

10 * 36 = 360

6x = 360

Divide both sides by 6.

x = 60

Now check your answer:636 636 10 x1060

If you cross multiply, you would have

360 360

Your turn:

4 x ___ = ___ 36180Dont forget that you can ALWAYS reduce a fraction!!4/36 will reduce down.but to what?

Divide by 2..4 2 = 2 36 2 = 18

But 2/18 can be further reducedagain, divide by 2 to become 1/9.

Now use 1/9 in the proportion.

1 x 9 180

9x 180

x 20

Checking your answer: 4 = x 36 180

4*180 = 720 x*36 = 36x

720 = 36x

20 = x

You can use proportions to solve real world problems. If you have 3 binders that are all the same size and they take up 4 inches on a shelf, how much shelf space would you need if you have 26 binders?

Start by setting up your first ratio:

Binders3Shelf space4

Then we use the same set up for the other ratio:

Binders26Shelf Space x

Make one proportion:

Binders: 326Shelf Space4 x

326 4 x

3x104

x 34 2/3

Homework:1) 7 63___ =___ x 54 2) 24 x ___ = ___ 21 35 3) 840 ___ = ___ 9xCarmen bought 3 pounds of peanuts for $1.08. Her friend also bought peanuts but spent $1.80. How many pounds of peanuts did her friend buy?