4. Lessons 6.2 and 6.3: Solving Proportions
Proportion: two ratios that are equal
Example:
NOTICE: Numerator units match
Denominator units match

5. The cross products of a proportion are equal.
28  2 =
4  14
a  d = b  c
56 = 56

6. Use cross products to solve for the variable.2) 1)
9(7) = 1.5b
63 = 1.5b
18t = (42)(3)
18t = 126
42 = b
b = 42
t = 7

7. 3)
Using Proportions to solve real life world problems.
REMEMBER: Top units (labels) must match and bottom units (labels) must match.
5(72) = 7x
360 = 7x
51.4 = x
x = 51.4

8. At a store, 5 erasers cost $2. 50. How many erasers can you buy for $7

9. In 2003 the exchange rate between the U. S
In 2003 the exchange rate between the U.S. and Canada was bout 3 Canadian dollars to 2 U.S. dollars. Cindy had 78 U.S. dollars to exchange when she visited Canada. How many Canadian dollars could she get in exchange?

10. Jewelers often mix gold with other metals
Jewelers often mix gold with other metals. A karat is a unit of measure that compares the mass of the gold in an object with the mass of the object. Karats are expressed as a number that is understood to be the numerator of a ratio whose denominator is 24. For examples, 24 karat gold means an object is pure gold, and 18 karat gold
means that or of the object is gold.
A 15 karat gold ring has a mass of 200 grams. How much gold is in the ring?

11. Homework: Worksheet