i feel like i should know this but i guess not

Question

There are 12 boxes stacked on a shelf. The height of each box is either 2 inches or 3 inches. The height of the stack of 12 boxes is 30 inches. Which system of equations can be used to find 

x, the number of 2-inch-thick boxes, and y, the number of 3-inch-thick boxes?

 

 

3x+2y = 30x+y = 12

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2x+3y = 12x+y = 30

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2x+3y = 30x+y = 12

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3x+2y = 12x+y = 30

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CLEAR ALL

Answer 1

There are 12 boxes stacked on a shelf. The height of each box is either 2 inches or 3 inches. The height of the stack of 12 boxes is 30 inches. Which system of equations can be used to find 

x, the number of 2-inch-thick boxes, and y, the number of 3-inch-thick boxes?

Let's write a system of equations based on what we know. First, we know there are 12 total boxes. However, we don't know the height of each box. So our first equation is x+y=12

Secondly, we know that the total height of the boxes is 30 inches, but we don't know how many of each box there are. We can write that as 2x+3y=30

So, our two equations are:

2x+3y=30

x+y=12

Answer 2

Let x be the number of 2 inch boxes and y be the number of 3 inch boxes. We have two unknowns, x and y, so we need two equations to solve it.

The number of boxes is 12: x + y = 12

The stack is 30 inches high: 2x + 3y = 30

Looks like the third set of equations in your list.