Answer: the number of black water bottles he has is 15
Step-by-step explanation:
Let x represent the number of white water bottles that he has.
Let y represent the number of black water bottles that he has.
The total number of water bottles is 20. It means that
x + y = 20
He sold a white water bottles for 1 and a black water bottles for 2 and earned a sum of 35. It means that
x + 2y = 35- - - - - - - - 1
Substituting x = 20 - y into equation 1, it becomes
20 - y + 2y = 35
- y + 2y = 35 - 20
y = 15
The number of white bottles = 5
The number of black bottles = 15
Let
x = the number of white bottles
y = the number of black bottles.
According to the question:
x + y = 20
1x + 2y = 35
From x + y = 20 we get y = 20 - x. Plug it in the other equation.
[tex]1x + 2y = 35\\x + 2(20-x) = 35\\x+40-2x=35\\x=5[/tex]
So, y = 20 - x = 20 - 5 = 15.
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