7'1: Using Proportions

1
7.1 Using Proportions

• Ratio any comparison of two numbers.
• Inches to Centimeters
• Life-size to scale drawing
• Miles to inches on a map
• Any ratio can be written as a fraction or with a
  colon
• Ex. If you make a scale drawing where 2 in.
  represents 10 ft., then you are using a scale of
  210 or 2/10 or 15 or 1/5

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• Being able to come up with the comparison is only
  half the problem. Often, we need to use two
  ratios set equal to each other to solve for a
  missing value.
• For example, you know 1.5 in. on the map
  represents 20 miles. If you measure your path on
  the map to be 5 in., how many miles is that?

3

• Proportion an equation involving two equal
  ratios. Use cross multiplication to solve.
• Remember the ratios must be in the same order!!
• Ex. Solve

4

• Ex. You look up the exchange rate and find that
  1 converts to 0.68. You travel to France with
  500, how many Euros do you have?
• There, you spend 100 and then fly to London
  where 1 converts to 0.75. How many Pounds do
  you have?

5

• You spend 100 and then fly back to the US
  knowing that 1 converts to 1.96. How many
  dollars do you have after your trip?

6

• In a triangle, the measures of the three angles
  are in a ratio of 243. Find the measure of
  each angle.