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Ratios. Special Fractions Mathematical ways to compare. Ratios?!?. Lets compare your height to weight. This ratio will be unique to you because your height and weight are unique.

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Ratios

Ratios

Special Fractions

Mathematical ways to compare.


Ratios1

Ratios?!?

Lets compare your height to weight. This ratio will be unique to you because your height and weight are unique.

A mathematical comparison between to measurable things. Written as a fraction of the measure of the first over the measure of the second.


Ratios2

Ratios?!?

Your ratio of height to weight

is 0.439

Put your height or 68 inches as the top number of a fraction and your weight or 155 pounds as the bottom number.


Special ratios

Special Ratios

There are certain ratios that allow us to change from one unit of measure to another without altering the original ratio. These ratios always equal 1 or the top always equals the bottom, they have equal measurements on top and bottom but in different units.


Using special ratios

Convert 3 yards to inches or 3 yards or

Using Special Ratios

Convert 2.5 dozen into donuts or 2.5 doz. or

donuts = 30 donuts

Convert 40 hours into days or

We use special ratios to convert from one unit of measurement to another. Multiply your current measurement by a special ratio. The old measurement will cancel out with itself on the bottom leaving you with the new. Notice the old unit must be on the bottom of the special ratio.

Convert 250 dollars into yearbooks or


Problems with ratios

Notice the two things that are equal; $73.70 and 5 lbs (you trade one for the other). The special ratio is or

Problems with Ratios

Convert 2 pounds to $ or

= $29.40 for 2 pounds

At the store, your favorite beef jerky costs $73.70 for 5 pounds. You only want 2 pounds, how much will you pay?

Make sure you put what you are converting from (lbs) on the bottom of the special ratio


Student practice 1

Student Practice #1

The side is on top because it comes first in the comparison.

Write a ratio for the comparison of:

The length of a side of a right triangle is 12 and the hypotenuse is 13


Student practice 2

Student Practice #2

Convert $45 to Euros or

= 32.40

Put the measurement you are changing on the bottom of the ratio

Write a special ratio then convert.

The current exchange rate is 25 dollars to 18 Euros

How many Euros do you get for 45 dollars?


Student practice 3

Student Practice #3

Convert 10 shovels of sand to cement or

=

Put the measurement you are changing on the bottom of the ratio

Write a special ratio then convert.

The mixture for your sidewalk is 1 shovel cement to 3 shovels of sand.

I have 10 shovels of sand, how many shovels of cement do I need?


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