Question 159819
Jack earned twice as much as Mary and Jill earned $8 more than Mary. Who made the most money? 
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Let M = amount Mary makes
then from: "Jack earned twice as much as Mary "
2M = amount Jack makes
and from: "Jill earned $8 more than Mary"
M+8 = amount Jill makes
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Notice that it would "appear" that 2M (the amount Jack makes) would be the most-- but, be careful...
What if M <= $8, say Mary makes $7
then 2M = $14 (Jack)
and M+8 = $15 (Jill)
Here, Jill makes the most.
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But if M = $9,
2M = $18 (Jack)
M+8 = $17 (Jill)
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Conclusion:Can't Answer
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A tire dealer sells 2 tires for as much as he paid for 3 tires. He paid $240 for a dozen tires. What is the total profit on 12 tires? 
Cost per tire: 240/12 = $20
Let P = profit of a single tire
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2(20+P) = 3(20)
40+2P = 60
2P = 20
P = $10
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Therefore, profit on 12 tires: 12*10 = $120