Question

You and some friends have $30. You want to order large pizzas (p) that are $9 each and drinks

Answer 1

Given:
Budget = $30
cost of pizza = $9
cost of drinks = $1
number of pizza = p
number of drinks = d

pizza and drinks should only be equal to or less than the budget of $30.

$9p + $1d < $30

unit cost of pizza :          9 
unit cost of drinks :         1
total cost of set (p & d) 10

pizza = 9/10 x 30 = 27 total cost of pizza
drinks =1/10 x 30 =   3 total cost of drinks

27 ÷ 9 = 3 number of pizzas to order 
  3 ÷ 1 = 3 number of drinks to order

To check:

9p + 1d < 30
9(3) + 1(3) < 30
27 + 3 < 30
30 < 30