One grade of tea costing $3.20 per pound is mixed with another grade costing $2.00 per pound to make 20 pounds of a blend that will sell for $2.72 per pound. How much of the $3.20 grade is needed? Formulate an
equation and then solve it to find how much of the $3.20 grade is needed.

X+y = 20... equation 1

3.2x + 2y = 54.4...equation 2

X= 12

12 of $3.2 grade is needed

Step-by-step explanation:

Let x = grade containing$ 3.2 per pound

Let y = grade containing $2.00 per pound

X+y = 20... equation 1

X3.2 +2y = 20(2.72)

3.2x + 2y = 54.4...equation 2

Multiplying equation 1 by 2

2x +2y = 40

3.2x + 2y = 54.4

1.2x = 14.4

X= 12

If x= 12

2x +2y = 40

2(12) + 2y = 40

2y = 40-24

2y = 16

Y= 8

starting with:    

5 + x - 12 = 2x - 7   

5 + x - 12 - x = 2x - 7 - x (subtract x from both sides)   

5 - 12 = x - 7 (combine and cancel x's from both sides)   

5 - 12 + 7 = x - 7 + 7 (add 7 to both sides)   

0 = x (add numbers together on both sides)       

so in order for the equation to be true, x must be 0.   

trying x = -0.5   

5 + x - 12 = 2x - 7 (original equation)   

5 + -0.5 - 12 = 2(-0.5) - 7 (plug in value of x)   

5 + -0.5 - 12 = -1 - 7 (did multiplication)   

-7.5 = -8 (did addition on both sides)       

since -7.5 is obviously not equal to -8, the value of -0.5 for x is wrong.   

trying x = 0   

5 + x - 12 = 2x - 7 (original equation)   

5 + 0 - 12 = 2(0) - 7 (plug in value of x)   

5 + 0 - 12 = 0 - 7 (did multiplication)   

-7 = -7 (did addition on both sides)       

since -7 equals -7, that demonstrates that the value of 0 for x is correct.   

trying x = 1   

5 + x - 12 = 2x - 7 (original equation)   

5 + 1 - 12 = 2(1) - 7 (plug in value of x)   

5 + 1 - 12 = 2 - 7 (did multiplication)   

-6 = -5 (did addition on both sides)       

since -6 is obviously not equal to -5, the value of 1 for x is wrong.