Transcript Homework for 7-4 - Stillman Valley High School

Homework for 7-4
p. 454 2, 4, 7, 10, 17, 20, 25, 32, 38,
43, 48, 52
7-4 Solve Linear Systems by
Multiplying First
Objective: solve linear systems by
elimination using multiplication first
Concessions
• A concession stand offers two different soft drink
specials. One special has 3 large drinks and 2
medium drinks for $15. The other has 2 large
drinks and 3 medium drinks for $13.75. Write a
system of linear equations to determine the cost
of each drink size.
• 3g + 2m = 15
• 2g + 3m = 13.75
• Can this system be solved using graphing?
Substitution? Elimination by +/-?
Solve Using Multiplication First
• 2x + y = -9
• 4x + 11y = 9
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x (-2) -4x - 2y = 18
4x + 11y = 9
9y = 27
y=3
2x + (3) = -9
2x = -12
x = -6
Solution is (-6, 3)
What would you need to multiply by to eliminate
y instead of x?
Solve the Linear System
• 2x – 3y = 6
• 4y = -7x – 8
• Put in standard form: 2x – 3y = 6
7x + 4y = -8
• What do we need to multiply by?
• Go ahead and solve!
• Solution is (0, -2)
Solve the Concessions Problem
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3g + 2m = 15
2g + 3m = 13.75
-6g – 4m = -30
6g + 9m = 41.25
5m = 11.25
m = 2.25
g = 3.5
The large drinks cost
$3.50; the mediums cost
$2.25.
Multiple Choice
• Mr. Alvarez bought a total of 20 pounds of grass seed
at the nursery for $168. He paid $9 per pound for
Kentucky bluegrass (k) and $6 per pound for Tall Fescue
(f). Which system of equations can be used to find the
amount of each that Mr. Alvarez purchased?
A. k + f = 168
9k + 6f = 20
B. k + f = 20
6k + 9f = 168
C. k + f = 168
6k + 9f = 20
D. k + f = 20
9k + 6f = 168
Answer: D