substitution method basics for beginners

With the equation: 2X + 3Y = 20, when Y = 5, we write...

• 2X + 5Y = 20

• 2X + 3(5) = 20

• 2X + 3(5Y) = 20

• None of the above

When the equation is: 5Y - 2X = 18 and Y = 3, we write

• 3Y -2X = 18

• 3Y -2(3) = 18

• 5(3) - 2X = 18

• 3- 2X = 18

With the equation: 5X - 2Y = 25, If X = 2, then...

• 52 - 2Y = 25

• 5X - 4 = 25

• 10 - 2Y = 25

• x = 10

If X = 3, and 1X - 2Y = 6, then...

• 3 - 2Y = 6

• 13 - 2Y = 6

• 3X - 2Y = 6

• 3X - 23 = 6

If 5X - 3Y = 22, and Y = 2, then I plug in a

• 2 where the X is

• 2 where the 3 is

• 2 where the Y is

• 2Y where the 3Y is

If X = 3, and X + Y = 12, then

• X + 3 = 12

• 3 + Y = 12

If X - 2Y = 10, and Y = 5, then

• X - 10 = 10

• X - 5Y = 10

• X - 25 = 10

If 4X + 4Y = 16, and Y = 2, then...

• I plug in a 2 for Y and get: 4X + 2Y = 16

• I plug in a 2 for Y and get: 4X + 4(2) = 16

• I plug in a 2 for Y and get: 4X + 42 = 16

• I plug in a Y for X and get: 4Y + 42 = 16

10X + 2Y = 20

X = 1, substitute and solve

• Y = 1

• Y = 2

• Y = 4

• Y = 5

2X - 4Y = 8

Y = 2,

Substitute and Solve

• X = 1

• X = 4

• X = 8

• X = 2

Tags

CCSS.8.EE.C.8B

CCSS.HSA.REI.C.6