Let’s solve each problem step by step.
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Problem 1: Given the function f(x) = 3x - x², find f(-2)
We plug in x = -2 into the function:
f(-2) = 3*(-2) - (-2)²
= -6 - (4)
= -6 - 4
= -10
✔ So the answer is
-10
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Problem 2: Bacteria growth — starts at 180, increases 22% per hour. How many after 4 hours? Use y = ab^x
Here:
- a = initial amount = 180
- b = growth factor = 1 + 0.22 = 1.22
- x = time in hours = 4
So:
y = 180 * (1.22)^4
First calculate 1.22^4:
1.22² = 1.4884
1.22^4 = (1.4884)² ≈ 2.2153
Now multiply:
180 * 2.2153 ≈ 398.75 → rounds to
399
✔ So the answer is
399
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Problem 3: Solve the inequality: -2(x - 3) > 36
Step 1: Distribute the -2:
-2*x + (-2)*(-3) > 36
→ -2x + 6 > 36
Step 2: Subtract 6 from both sides:
-2x > 30
Step 3: Divide by -2 — remember to flip the inequality sign when dividing by negative!
x < -15
✔ So the answer is
x < -15
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Problem 4: Solve the system:
3x - y = 17
-x + y = -7
Add the two equations together to eliminate y:
(3x - y) + (-x + y) = 17 + (-7)
→ 2x = 10
→ x = 5
Now plug x = 5 into one of the equations, say the second:
-x + y = -7
→ -5 + y = -7
→ y = -2
✔ So the solution is
(5, -2)
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Problem 5: Sequence: 4, 1, -2, -5. What is the 65th term?
This is an arithmetic sequence.
First term a = 4
Common difference d = 1 - 4 = -3
Formula for nth term:
a_n = a + (n - 1)d
So for n = 65:
a_65 = 4 + (65 - 1)(-3)
= 4 + 64*(-3)
= 4 - 192
= -188
✔ So the answer is
-188
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Final Answer:
1. B
2. A
3. C
4. B
5. C
Parent Tip: Review the logic above to help your child master the concept of algebra for eighth grade worksheet.