1. Lesson 8.1B

2. Inverse or direct?
1a) x = running speed y = how long it takes to finish a marathon b) x = typing speed y = how many pages you can type in an hour

3. Inverse or direct? 2. a) 3x = y b) y = 27 𝑥 c) y = x + 2 d) xy = 15

4. Inverse or direct?
3. a) b) c)

5. Inverse or direct?
a) x y b) x y c) x y a = ? a = ? a = ? y = y = y =

6. Application
The number of songs that can be stored on an iPod varies inversely with the average size of a song.
One iPod can store 16,000 songs when the average song size is 4 megabytes.
Write a model.
How many songs could be stored if the average song size were 5.7 megabytes?

7. EXTRA CREDIT
If it takes 5 kids 30 minutes to eat 10 pieces of pizza, how long should it take 15 kids to eat 50 pieces of pizza? 50 minutes

8. Joint Variation z = axy If z varies jointly with x and y, then
If z = 60 when x = 3 and y = 5,
Find the constant of variation, a
Write an equation
Find z when x = 2 and y = 7

9. The amount of heat lost through a window pane varies jointly with the area of the pane and the temperature difference on opposite sides of the window. When the temperature difference is 70 degrees, a 12 square foot window loses 950 BTUs. Find the amount of heat lost through a 16 square foot window when it is 70 degrees inside and 30 degrees outside.

10. Write an Equation y varies inversely with x
z varies jointly with x, y, and r
y varies inversely with the square of x
z varies directly with y and inversely with x
x varies jointly with t and r and inversely with s