# Writing Formulas and Substituting in a Formula

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8.1Writing Formulas and Substituting in a Formula

## Writing Formulas and Substituting in a Formula Revision Questions

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1. .A certain product costs \$37 per item plus \$2 shipping cost. What is the formula that gives the total cost C for ordering N items from this product?

1. C = 37 (2 + N)
2. C = 37N + 2
3. C = N(37 + 2)
4. C = 37 + 2N

2. .What is the variable y in the formula

y = a - b/1 - c/

if a = 8, b = 5 and c = 4?

1. -1
2. 1
3. 2
4. 1/7/

3. .What is the formula applied in the spreadsheet shown below?

1. y = x + 8
2. y = 2(x + 3)
3. y = 2x + 3
4. y = 3x - 2

4. .A car is moving at v0 = 20m/s when the driver sees an obstacle in front of him. It takes him t = 1.2 s to press the brakes. The car eventually starts decelerating uniformly at a = -5 m/s2. How far from the initial position will the car stop? Use the formulas d = v0t for uniform motion and v2 - v02 = 2ad for the uniformly decelerated one.

1. 24 m
2. 40 m
3. 64 m
4. 84 m

5. .What is the inverse formula of

y = 4 - 2x
1. y = 2 - 4x
2. x = 2 - 4y
3. x = 4 - 2y
4. x = 2 - y/2

6. .What is the maximum value of y in the formula

y = 9 - x2
1. -3
2. 0
3. 9
4. 27

7. .The number N of bacteria per square millimetre in a sample decreases when using a new antibiotic according the formula

N(t) = N0 ∙ 2-0.6t

where N0 is the initial number of bacteria in the sample and t is the time in hours.

Calculate the number of bacteria per square millimetre left in the sample 5 hours after starting the cure if the original number of bacteria was 6,432.

1. 6,424
2. 804
3. 604
4. 101

8. .What is the value of z in the formula

y = 3x2 -z/2+5/

if x = 2 and y = 10.

1. 5
2. 7
3. 10
4. 14

9. .What is the value of x in the formula

y = 5 - x3

if y = -3?

1. -22
2. 2
3. 32
4. -2

10. .The products A, B and C in a market had a discount of 10%, 20% and 30% respectively. What is the formula that gives the new cost Y when purchasing one item from each product?

1. Y = 90A + 80B + 75C
2. Y = (0.1 + 0.2 + 0.25)(A + B + C)
3. Y = 0.1A + 0.2B + 0.25C
4. Y = 0.9A + 0.8B + 0.75C

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