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# Finding Ratio Amounts in Proportions

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### Finding Ratio Amounts in Proportions

1. 1. Images Source: Google Images
2. 2. A strawberry milkshake is made in the ratio of 2 partsstrawberry ice cream to 7 parts of milk.If we fill our blender with 3 scoops of ice cream,then how many scoops of milk shouldwe add to the blender? Ice Cream : Milk 2 : 7 3 : m Image Source: Google ImagesWhere m = scoops of Milk (Continued next slide)
3. 3. We can solve this question using a method called“Cross Multiplying” like this: Ice Cream : Milk 2 : 7 3 : m 2xm=3x7 Image Source: Google Images 2m = 21 2 2 m = 10.5 scoops of milk
4. 4. - Write the Ratios out Vertically- Make sure there are three numbers present and one unknown letter variable- Cross Multiply the Items- Divide both sides by the number which is in front of the letter variable- Write the simplified answer
5. 5. a : 15 = 2 : 5 Find the value of “a” 2 : 5 Write the ratios out vertically, and then Cross Multiply a : 152 x 15 = 5 x a (Note writing 2 x 15 = a x 5 is also okay) 30 = 5a “5” is the number in front of the letter variable and so divide 30 = 5a both sides of the equals sign 5 5 by 5 and simplify. 6=a a=6
6. 6. 4 : 11 = 80 : k Find the value of “k” 4 : 11 Write the ratios out vertically, and then Cross Multiply80 : k4 x k = 11 x 80 (Note writing k x 4 = 80 x 11 is also okay) 4k = 880 “4” is the number in front of the letter variable and so divide 4k = 880 both sides of the equals sign 4 4 by 4 and simplify. k = 220
7. 7. The instructions for mixing two stroke lawn mower fuelsay to mix 1 part Oil to 24 parts Petrol or Gasoline fuel.If we have a 200ml of Oil, then how much Petrol dowe need to add to make two stroke lawn mower fuel ?Note that the usual method for makingthe fuel is to first pour the oil into a 5litre fuel can, and then add the requiredamount of petrol in stages, giving the cana good shake, with the lid on, to mix thefuel thoroughly at the end of each stage.(Continued next slide) Image Source: http://www.hobuk.co.uk
8. 8. Oil : Petrol = 1 : 24 = 200 : P where “P” = Petrol Amount 1 : 24 Write the ratios out vertically, and then Cross Multiply 200 : P 1 x P = 24 x 200 1P = 4800 “1” is the number in front of the letter variable and so divide 1P = 4800 both sides of the equals sign 1 1 by 1 and simplify, or do 1P = PP = 4800ml or 4.8 litres (So we just fill the 5 litre can with Petrol)
9. 9. Famous Australian artist Ken Done has created the following designsfor a new Australian flag.The ratio for the flag size is Length : Width = 5 : 3Tiffany is going to make one of these flags for her Graphic DesignProject, and plans for the length of the flag to be 90 cm long.What width should she make the flag ?(Continued next slide) Image Source: http://www.ausflag.com.au
10. 10. Length : Width = 5 : 3 = 90 : w where “w” = Width of Flag 5 : 3 Write the ratios out vertically, and then Cross Multiply 90 : w 5 x w = 3 x 90 5w = 270 “5” is the number in front of the letter variable and so divide 5w = 270 both sides of the equals sign 5 5 by 5 and simplify. w = 54 cm