A merchant has coffee worth $70 a pound that she wishes to mix with 40 pounds of coffee worth $90 a pound to get a mixture that can be sold for $80 a pound. How many pounds of the $70 coffee should be used?

40 pounds

Step-by-step explanation:

Let assume that the first coffee = F worth $70 a pound. That is 70F

to mix with the second coffee S 40 pounds of coffee worth $90 a pound. That is 40 × 90 = 3600

to get a mixture M that can be sold for $80 a pound. That is 80(40 + F)

M = F + S

80(40 + F) = 3600 + 70F

3200 + 80F = 3600 + 70F

10F = 400

F = 40 pound

answer:

it is general formula that is used to write value to its excet position

a11 a12 a13

a21 a22 a23

it is the example of order 2 by 3 matrix in this

a11 means value occur in 1 st row 1st column

a12 means value occurs in 1st row 2nd column

a13 means value occur in 1st row and 3rd column

a21 means value occurs in 2nd row and 1st column

a22 means value occurs in 2nd row and in 2nd column

a23 means value occurs in 2nd row and in 3rd column