Let's say Mary's brother's age is x and Mary's age is y
(1) x = 3y - 5
(2) x + y = 39
Now if we substitute equation (1) into equation (2) we get:
3y - 5 + y = 39
4y = 44
y = 11
Therefor Mary is 11 years old
They can rent the boat for 4 hours if they spend 700 dollars.
Answer: The cost for one hamburger is $2.5
Step-by-step explanation:
Let x represent the cost of one hamburger.
Let y represent the cost of one fry.
The tennis coach took his team out for lunch and bought eight hamburgers and five fries for $24. This means that
8x + 5y = 24- - - - - - - - - - - -1
The players were still hungry so the coach bought six more hamburgers and two more fries for 16.60. It means that
6x + 2y = 16.6- - - - - - - - - - 2
Multiplying equation 1 by 6 and equation 2 by 8, it becomes
48x + 30y = 144
48x + 16y = 132.8
Subtracting, it becomes
14y = 11.2
y = 11.2/14
y = 0.8
Substituting y = 0.8 into equation 1, it becomes
8x + 5 × 0.8 = 24
8x + 4 = 24
8x = 24 - 4 = 20
x = 20/8
x = 2.5
