Answer: the price of a bottle of water is $1.5
Explanation:
Let x represent the price of one pretzel.
Let y represent the price of one bottle of water.
At the shopping mall, Joaquin bought 4 pretzels and a bottle of water for 11.50. It means that
4x + y = 11.5- - - - - - - - - -1
Kelly bought 3 pretzels and a bottle of water for 9.00. It means that
3x + y = 9- - - - - - - - - - - - 2
Subtracting equation 2 from equation 1, it becomes
x = 2.5
Substituting x = 2.5 into equation 1, it becomes
4 × 2.5 + y = 11.5
10 + y = 11.5
y = 11.5 - 10
y = 1.5