Using Proportions

1
Using Proportions

• Ratios

2
Ratios Review

• Ratios are comparisons between two numbers.
• Format
• 4 to 5 45 4/5
• WeedEater
• Mix 2 ounces of oil for every 50 ounces of gas.
• What is the gas to oil ratio?

3
Write a Ratio

• In a new car dealers lot, there were 23 silver,
  18 white, 2 maroon, 8 red, and 12 blue vehicles.
• Write the ratio of silver vehicles to total
  vehicles.
• Write the ratio of white to blue vehicles.

23
63
18
12
4
Using Proportions to Solve Problems
5
Proportion

• A proportion is an equation that says one ratio
  is equal to another.

ratio
ratio

6
Solve Proportions

• When 3 of the 4 values are known in a proportion,
  we must solve for the missing number.

18
7

x
5
18 x 5 90
90 7
12.9
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Proportions 1 of 4

• If you drive 90 miles in 2.5 hrs, how long should
  it take for you to complete the final 200 miles
  of a trip?

miles
90 mi
200 mi

hours
2.5 hr
? hr
Answer 5.6 hrs
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Proportions 2 of 4

• Six identical CNC machines can produce 768
  pistons in one day. If two of the CNC machines
  break down, how many pistons can be produced in a
  day?

machines
6 CNC
4 CNC

pistons
768 pistons
? pistons
Answer 512 pistons
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Proportions 3 of 4
Answer 203.1 mph

• A 48 second lap at a large racetrack reflects an
  average lap speed of 195 mph. If a car completes
  a lap in 50 seconds, what is the average lap
  speed?

time (sec)
48 sec
50 sec

avg. speed (mph)
195 mph
? mph
10
Proportions 3 of 4
Answer 187.2 mph

• A 48 second lap at a large racetrack reflects an
  average lap speed of 195 mph. If a car completes
  a lap in 50 seconds, what is the average lap
  speed?

time (sec)
48 sec
? mph

avg. speed (mph)
195 mph
50 sec
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Proportions 4 of 4

• Three employees can complete a basic auto
  interior restoration in 5 work days. If only two
  employees are available for a similar project,
  how long will it take?

3 emp.
? days

5 days
2 emp.
Answer 7.5 days
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Practice

• Complete the Worksheet