Introduction to Ratios


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Introduction to Ratios

  1. 1. If you have ridden a bike lately, then you will know that for goingdownhill very fast, we use a Rear Cog that does not have as manyteeth compared to the Front Chain Ring.This gives us a "Very High" Gear Ratio of 53 to 11.Front / Rear gear measurement uses two numbers (e.g. 53/11) wherethe first is the number of teeth in the front chain ring and the second isthe number of teeth in the rear sprocket.Low Gear Ratios are needed for going up hills, and a low gearRear / Front Ratio might typically be 34 / 23, or 34 teeth on the rearcog, compared to 23 teeth on the front chain ring.In Low Gear the chain ring will rotate more times than the cog, whichgives us more power supplied to a single revolution of the rear wheel.This makes it easier to get up a big hill.
  2. 2. Image Source: http://blog.jeffersonatwesttown.lincolnapts.comRatios are very important in Cooking.If a recipe calls for 1 egg and 2 cups of flour, the relationship ofeggs to cups of flour is 1 to 2.Add the wrong ratios of ingredients to a baked cookies recipe,and the resulting salty rock hard cookies will not be a hit with anyone!
  3. 3. Image Source: Ratios are also important in making gold for jewelery.For example 14 carat Gold can be made by combining 6 parts Gold withtwo and a half parts Copper, and one and a half parts Silver. The Ratio of Gold to Copper to Silver = 6 to 2.5 to 1.5
  4. 4. A Ratio is a comparison or a relationship between two items. The Ratio of Blue Circles to Pink Circles is five blue circles compared to three pink circles. We can write this in any three of the following ways: Blue to Pink = 5 to 3 or 5:3 or 5/3
  5. 5. We can express our Ratio comparison in two ways : Blue Circles to Pink Circles or Pink Circles to Blue CirclesBlue to Pink = 5 to 3 or 5:3 or 5/3Pink to Blue = 3 to 5 or 3:5 or 3/5
  6. 6. If we double our circles we now have 10 Blue circles to6 Pink circles. There are still 5 Blue Circles for every threePink circles. We simply now have two of these groupings.This means the simplest Ratio we can write for our situationis Blue to Pink = 5 : 3. The Ratios 10 : 6 and 5 : 3 are said to be “Equivalent”.
  7. 7. What is the Ratio of Cats to Snakes in this Picture ?There are two cats and one snake, so the ratio is 2 to 1. The Ratio answer is Cats : Snakes = 2 : 1 Image Source: istockphoto Purchased by Passy’s World
  8. 8. What is the Ratio of Apples to Bananas ?There are 5 apples and 6 bananas, so the ratio is 5 to 6. The Ratio is Apples : Bananas = 5 : 6 Image Source: Free Clipart Images from
  9. 9. What is the Ratio of Boys to Girls ?There is one boy and three girls, so the ratio is 1 to 3 . The Ratio is Boys : Girls = 1 : 3 Image Source: Free Clipart Images from
  10. 10. Write 10kg to 3kg in “shorthand ratio” form.There are ten kilograms compared to three kilograms . The “Shorthand Ratio” = 10 : 3 Image Source: Free Clipart Images from
  11. 11. The items being compared in a Ratio must always be in the same units.For example: 1km to 300m needs to be written as 1000m to 300m,which in shorthand form is 1000 : 300123 days to 1.2 years needs to be converted into123 days to (1.2 x 365) days = 123 : 43827 minutes to 2 hours needs to be converted into27 minutes to (2 x 60) minutes = 27 : 120 Note that we always convert both items into the smaller unit.(Meters are smaller than kilometers, days are smaller than years,minutes are smaller than hours, days are smaller than weeks, and so on.
  12. 12. Visit our site for Free Mathematics PowerPoints