1. 3.2 Ratios and Proportions

2. Ratio
ratio – a comparison of 2 quantities. The ratio of a to b (b ≠ 0) can be written: a to b a:b

3. Ex. Write as a ratio: (a) 40 mi to 30 mi (b) 50 min to 2 hr (c) 6 dollars to 3 dollars
Need same units

4. Proportions
proportion – 2 ratios that are equal. “a is to b as c is to d” Cross Products

5. Solving Equations Using Cross Products (works only if you have a proportion – 1 term per side)
Ex. Solve: 4(x) = 6(18) 4x = x = 27 {27}
Ex. Solve: 3(3m – 2) = 5(4 – m) 9m – 6 = 20 – 5m 9m – 6 + 5m = 20 – 5m + 5m 14m – 6 = 20 14m – = m =

6. Ex. If 7 shirts cost $87. 50, find the cost of 11 shirts. 7(x) = 11(87
Ex. If 7 shirts cost $87.50, find the cost of 11 shirts. 7(x) = 11(87.50) 7x = x = Ans: $137.50

7. Ex. The tax on a property with an assessed value of $65,000 is $720
Ex. The tax on a property with an assessed value of $65,000 is $720. Find the tax on a property with an assessed value of $162, ,500(720) = 65,000(x) 117,000,000 = 65,000x 65,000 65,000 x = 1,800 Ans: value is $1,800

8. Groups
Pages 200 – 201: 9, 11, 22, 27, 35, 48