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The sum of two numbers is -9 and their difference is 31. What are the numbers?

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Let x = 1st number
y = 2nd number
1). x + y = -9
2). x - y = 31
Solve 1) for x, x = -9 -y
Substitute that into 2) for x & solve
-9 - y - y = 31
-9 - 2y = 31
+9. +9
-2y = 40
/-2. /-2
y = -20

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1. A diver's total score is the sum of the scores of his 6 dives. Estimate the total score for a diver whose dive scores were 87.6, 88.3, 91.3, 92.0, 88.3, and 89.9 points.
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2. Short Response: Lydia earned \$9.75 per hour as a lifeguard last summer. She worked 24 hours a week.

a. About how much did Lydia make in a week?

b. About how much did Lydia earn in 8 weeks?

c. Lydia is hoping to make \$2600 this summer. About how many more weeks does she need to work to reach her goal?
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-40 + 31= -9

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The numbers are 11 and -20.
x+y=-9
x-y=31I
x=-9-y
-9-2y=31
-2y=40
y=-20
x=11