Week 9, Day Two
Videos for section 3-4 AND p. 132 # 1-11 all
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keyword: MT8CA 3-4
Warm up a) 5n + 3n – n + 5 = 26 b) -81 = 7k + 19 + 3k c) 37 = 15a-5a-3 d) Lydia rode 243 miles in a three-day bike trip. On the first day, Lydia rode 67 miles. On the second day, she rode 92 miles. How many miles per hour did she average on the third day if she rode for 7 hours?

a) 5n + 3n – n + 5 = 26 n=3 b) -81 = 7k + 19 + 3k k=-10 c) 37 = 15a-5a-3 a=4 d) Lydia rod 243 miles in a three-day bike trip. On the first day, Lydia rode 67 miles. On the second day, she rode 92 miles. How many miles per hour did she average on the third day if she rode for 7 hours?
12 mi/h

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Additional Example 1A: Solving Equations with Variables on Both Sides
Solve.
4x + 6 = x
4x + 6 = x
– 4x – 4x
To collect the variable terms on one side, subtract 4x from both sides.
6 = –3x
–3
6
=
–3x
–3
–2 = x
Since x is multiplied by -3, divide both sides by –3.

Helpful Hint
You can always check your solution by substituting the value back into the original equation.

Additional Example 1B: Solving Equations with Variables on Both Sides
Solve.
9b – 6 = 5b + 18
9b – 6 = 5b + 18
– 5b – 5b
4b – 6 = 18
+ 6 + 6
4b = 24
4b
4
=
24
4
b = 6
To collect the variable terms on one side, subtract 5b from both sides.
Since 6 is subtracted from 4b, add 6 to both sides.
Since b is multiplied by 4, divide both sides by 4.

Additional Example 1C: Solving Equations with Variables on Both Sides
Solve.
9w + 3 = 9w + 7
9w + 3 = 9w + 7
– 9w – 9w To collect the variable terms on one side, subtract
9w from both sides.
3 ≠ 7
There is no solution. There is no number that can be substituted for the variable w to make the equation true.

Helpful Hint if the variables in an equation are eliminated and the resulting statement is false, the equation has no solution.

Solve.
5x + 8 = x
5x + 8 = x
– 5x – 5x
–4
8
8 = –4x
=
–4x
–4
–2 = x
Check It Out!
Example 1A
To collect the variable terms on one side, subtract 5x from both sides.
Since x is multiplied by –4, divide both sides by –4.

Solve.
3b – 2 = 2b + 12
3b – 2 = 2b + 12
– 2b – 2b
b – 2 = 12
+ 2 + 2 b = 14
Check It Out!
Example 1B
To collect the variable terms on one side, subtract 2b from both sides.
Since 2 is subtracted from b, add 2 to both sides.

Check It Out!
Example 1C
Solve.
3w + 1 = 3w + 8
3w + 1 = 3w + 8
– 3w – 3w To collect the variable terms on one side, subtract
3w from both sides.
1 ≠ 8
No solution. There is no number that can be substituted for the variable w to make the equation true.

To solve more complicated equations, you may need to first simplify by combining like terms or clearing fractions. Then add or subtract to collect variable terms on one side of the equation. Finally, use properties of equality to isolate the variable.

Additional Example 2A: Solving Multi-Step Equations with Variables on Both Sides
Solve.
10z – 15 – 4z = 8 – 2z – 15
10z – 15 – 4z = 8 – 2z – 15
+ 2z
6z – 15 = –2z – 7
+ 2z
8z – 15 = – 7
+ 15 +15
8z = 8
8z 8
=
8
z = 1
8
Combine like terms.
Add 2z to both sides.
Add 15 to both sides.
Divide both sides by 8.

Additional Example 2B: Solving Multi-Step Equations with Variables on Both Sides y
5
+ –
3y
5
= y –
3
4
7
10 y
5
+ –
3y
5
= y –
3
4
7
10
20
( y
5
+ –
) 3y
5 = 20
( )
20
( ) y
5 + 20
( )
– 20
( )
= 20(y) – 20
3 ( )
7
10
4y + 12y – 15 = 20y – 14
Multiply by the LCD, 20.
7
10
16y – 15 = 20y – 14 Combine like terms.

Additional Example 2B Continued
16y – 15 = 20y – 14
– 16y – 16y
–15 = 4y – 14
+ 14 + 14
–1 = 4y
–1
4
=
–1
4
= y
4y
4
Subtract 16y from both sides.
Add 14 to both sides.
Divide both sides by 4.

Solve.
12z – 12 – 4z = 6 – 2z + 32
Check It Out!
Example 2A
12z – 12 – 4z = 6 – 2z + 32
+ 2z
8z – 12 = –2z + 38
+ 2z
10z – 12 = 38
+ 12 +12
10z = 50
10z 50
=
10
z = 5
10
Combine like terms.
Add 2z to both sides.
Add 12 to both sides.
Divide both sides by 10.

Check It Out!
Example 2B y
4
5y
6
3
4 y
4
5y
6
3
4
24
( y
4
) 5y
6 = 24
( )
6
8
6
8
24
( ) y
4 + 24
( )
+ 24
( )
= 24(y) – 24
3 ( )
6
8
6y + 20y + 18 = 24y – 18
26y + 18 = 24y – 18
Multiply by the LCD, 24.
Combine like terms.
6
8

Check It Out!
Example 2B Continued
26y + 18 = 24y – 18
– 24y – 24y
2y + 18 = – 18
– 18 – 18
2y = –36
2y
2
=
–36
2
y = –18
Subtract 24y from both sides.
Subtract 18 from both sides.
Divide both sides by 2.

Additional Example 3: Business Application
Daisy ’ s Flowers sells a rose bouquet for $39.95 plus $2.95 for every rose. A competing florist sells a similar bouquet for $26.00 plus $4.50 for every rose. Find the number of roses that would make both florists' bouquets cost the same price.
What is the price?
Write an equation for each service. Let c represent the total cost and r represent the number of roses.
total cost is flat fee plus cost for each rose
Daisy ’ s: c = 39.95 + 2.95 r
Other: c = 26.00 + 4.50 r

Additional Example 3 Continued
Now write an equation showing that the costs are equal.
39.95 + 2.95r = 26.00 + 4.50r
– 2.95r – 2.95r
Subtract 2.95r from both sides.
39.95 = 26.00 + 1.55r
– 26.00
– 26.00
13.95 = 1.55r
13.95
1.55
=
1.55r 1.55
Subtract 26.00 from both sides.
Divide both sides by 1.55.
9 = r
The two bouquets from either florist would cost the same when purchasing 9 roses.

Additional Example 3 Continued
To find the cost, substitute 9 for r into either equation.
Daisy ’ s:
c = 39.95 + 2.95r
c = 39.95 + 2.95( 9 )
c = 39.95 + 26.55
c = 66.5
Other florist:
c = 26.00 + 4.50r
c = 26.00 + 4.50(
c = 26.00 + 40.50
c = 66.5
9
The cost for a bouquet with 9 roses at either florist is $66.50.
)

Check It Out!
Example 3
Marla ’ s Gift Baskets sells a muffin basket for $22.00 plus $2.25 for every balloon. A competing service sells a similar muffin basket for $16.00 plus $3.00 for every balloon.
Find the number of balloons that would make both baskets cost the same price.
Write an equation for each service. Let c represent the total cost and b represent the number of balloons.
total cost is flat fee plus cost for each balloon
Marla ’ s: c = 22.00 + 2.25 b
Other: c = 16.00 + 3.00 b

Check It Out!
Example 3 Continued
Now write an equation showing that the costs are equal.
22.00 + 2.25b = 16.00 + 3.00b
– 2.25b – 2.25b
Subtract 2.25b from both sides.
22.00 = 16.00 + 0.75b
– 16.00
– 16.00
6.00 = 0.75b
6.00
0.75
=
0.75b 0.75
Subtract 16.00 from both sides.
Divide both sides by 0.75.
8 = b
The two services would cost the same when purchasing a muffin basket with 8 balloons.