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Systems and Equations

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1. What is a system of equations?

2. Solve for X and Y in the following problems using either substitution or elimination methods. Make sure you show all your work so you can get partial credit even if your final answer is wrong.

a. X + Y = 10 , 3X + Y = 12

b. 2X + 5Y = 19 , 3X + 3Y = 15

c. 4X + Y = 22 , 2X + 3Y = 16

d. 12X + Y = 174 , 8X - 2Y = 36

3. Suppose Bob owns 2,000 shares of Company X and 10,000 shares of Company Y. The total value of Bob's holdings of these two companies is $372,000.

Suppose Frank owns 8,000 shares of Company X and 6,000 shares of Company Y. The total value of Franks holdings of these two companies is $400,000.

a. Write equations for Bob and Frank's holdings. Use the variables X and Y to represent the values of shares of Company X and Company Y.

b. Solve for the value of a share of Company X and Company Y. Show your work so you can get partial credit even if your final answer is wrong.

4. Solve for X, Y, and Z in the following systems of three equations using either substition or elimination methods:

a. X + 2Y + Z = 22

X + Y = 15

3X + Y + Z = 37

b. 10X + Y + Z = 603

8X + 2Y + Z = 603

20X - 10Y - 2Z = -6

c. 22X + 5Y + 7Z = 12

10X + 3Y + 2Z = 5

9X + 2Y + 12Z = 14

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Systems and Equations are assessed.

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1. What is a system of equations?

A system of equations is a collection of two or more equations with a same set of unknowns.

2. Solve for X and Y in the following problems using either substitution or elimination methods. Make sure you show all your work so you can get partial credit even if your final answer is wrong.

a. X + Y = 10 , 3X + Y = 12

if we multiply 2nd equation by -1;
X + Y = 10
-3X - Y = -12

now add them together;
X-3X+Y-Y=10-12
-2X=-2
X=1

and now we can find Y from either one of the equations by substituting X=1;

1+Y=10
Y=9

b. 2X + 5Y = 19 , 3X + 3Y = 15

from the first equation;
2X=(19-5Y)
X=(19-5Y)/2

substitude X in 2nd equation;

3(19-5Y)/2+3y=15
(57-15Y)/2+6Y/2=15
(57-15Y+6Y)/2=15
57-9Y=30
9Y=27
Y=3

and solve for X;
3X+3(3)=15
3X=15-9
3X=6
X=2

c. 4X + Y = 22 , 2X + 3Y = 16

mutiply 2nd equation by -2;

4X + Y = 22
-4X ...

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