The 3x3 identity matrix is 

Both scalar multplication of a matrix and matrix addition are performed elementwise, so

 is the second element in the second row, which is 6; similarly, . The equation becomes

When multiplying a constant to a matrix, multiply each entry in the matrix by the constant.

M_2x3 x N_3x4 = P_2x4 

In general matrix notation, M_rxc shows that the matrix is named M and r is the number of rows and c is the number of columns.  When multiplying two matrices, the number of columns in the first matrix must match the number of rows in the second matrix.  In addition, when adding or subtracting matrices, the matrices must be of the same size.

In order to solve the matrix, the determinant rule "ad-bc" must be used.  is in the "a" position,  is in the "b" position,  is in the "c" position, and  is in the "d" position. After plugging the numbers into "ad-bc," we get

To set up and augmented matrix for a 3x3 system of equations, all equations must be in standard form . The third equation is already in standard form; the first two are not and must be rewritten as such.

The system is now

Write the augmented matrix with each row comprising the coefficients of one equation in order:

is the correct choice.

To set up and augmented matrix for a 2x2 system of equations, both equations must be in standard form . The second equation is already in standard form.

Rewrite the first equation in standard form as follows:

The system has been rewritten as

Write the augmented matrix with each row comprising the coefficients of one equation in order:

is the correct choice.

If we let , , and  represent the number of large, medium, and small boxes sold, respectively, since twenty more medium boxes than large were sold, one equation of the 3x3 system will be

or, in standard form,

Since 445 boxes were sold, another linear equation will be

The money raised from the sale of  large boxes of cookies, each of which cost $5.75, is ; the money raised from the sale of  small boxes of cookies, each of which cost $4.75, is ; and the money raised from the sale of  small boxes of cookies, each of which cost $3.25, is . 

The total money raised is $1,924.25, so the other linear equation of the system is 

The augmented matrix of this system will comprise the coefficients of these equations, all of which are now standard form, so the matrix will be

,

which is the correct choice.

If we let  and  represent the number of large and small boxes sold, respectively, since 305 boxes were sold, one linear equation of the 2x2 system will be

The money raised from the sale of  large boxes of cookies, each of which cost $4.75, is ; the money raised from the sale of  small boxes of cookies, each of which cost $3.25, is . The total money raised is $1,196.75, so the other linear equation of the system is 

The augmented matrix of this system will comprise the coefficients of these equations, both of which are in standard form, so the matrix will be

If we let  and  represent the amount of the weaker and stronger solutions, respectively, since the chemist needs 1 liter of the resulting solution, one linear equation of the 2x2 system will be 

The amount of alcohol in  liters of a 10% solution will be ; the amount of alcohol in  liters of a 40% solution will be ; and the total amount of alcohol in the resulting solution will be 20 % of a liter, or 0.20 liters. Therefore, the second linear equation of the system will be

The augmented matrix of this system will comprise the coefficients of these equations, both of which are in standard form, so the matrix will be

,

which is the correct choice.

To find the number of blue items Jon has, we sum the entries in the column labelled  and get . Recall that matrices are organized by rows and columns where each entry refers to the number of items that are, in this case, both of the same color AND type. All the entries in any one column are of the same color. All of the entries in any row are of the same clothing type.