1. Matrix Multiplication, Part 2a V T S Pizza Drink Salad What if your group wants to buy 1 pizza, 3 drinks, and 3 salads? Or 2 pizzas, 4 drinks, and 3 salads? Or 3 pizzas, 4 drinks, and 2 salads? How much will the total cost be?

2. Matrix Multiplication, Part 2a V T S Pizza Drink Salad We can solve this using matrices, but we need to be careful how we set them up. Remember that the columns of the 1 st matrix have to match up with the rows of the 2 nd matrix.

3. Matrix Multiplication, Part 2a V T S Pizza Drink Salad The matrix we have so far relates the cost of the three food items to the three different pizzerias. The other matrix will relate the quantity of each food item. What do the two matrices share in common?

4. Matrix Multiplication, Part 2a V T S Pizza Drink Salad They both contain the three food items. Therefore, the food items should be in the columns of the 1 st matrix and rows of the 2 nd.

5. Matrix Multiplication, Part 2a V T S Pizza Drink Salad Plan 1 Plan 2 Plan 3 P D S X

6. Matrix Multiplication, Part 2a V T S Pizza Drink Salad The 1 st element = 1(11.25) + 3(1.09) + 3(3.69) = 25.59 Plan 1 Plan 2 Plan 3 P D S X

7. Matrix Multiplication, Part 2a V T S Pizza Drink Salad The entire product matrix is: Plan 1 Plan 2 Plan 3 P D S X

8. Matrix Multiplication, Part 2a V T S Pizza Drink Salad The entire product matrix is: Plan 1 Plan 2 Plan 3 P D S X What do those numbers mean?

9. Matrix Multiplication, Part 2a V T S Pizza Drink Salad Plan 1 Plan 2 Plan 3 P D S X Use the row headings of the 1 st matrix and the column headings of the 2 nd matrix.

10. Matrix Multiplication, Part 2a V T S Plan 1 Plan 2 Plan 3 How much would Plan 2 cost at Sal’s?

11. Matrix Multiplication, Part 2a V T S Plan 1 Plan 2 Plan 3 How much would Plan 2 cost at Sal’s? $41.05