Mathematics
Grade 11
15 min
Multiply three or more numbers: word problems
Multiply three or more numbers: word problems
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1
Introduction & Learning Objectives
Learning Objectives
Deconstruct complex word problems involving angle measures to identify all relevant numerical factors.
Apply formulas for angular velocity, sector area, and complex number rotation to set up multiplication expressions with three or more terms.
Perform calculations involving the multiplication of integers, decimals, fractions, and constants like π.
Correctly manage and convert between units of angle measure (degrees and radians) within a multi-step problem.
By the end of a this lesson, students will be able to interpret the product of multiple factors as a meaningful quantity in a geometric or physical context.
Formulate and solve problems involving sequential transformations or cumulative effects related to angles.
How does a tiny motor spin a giant Ferri...
2
Key Concepts & Vocabulary
TermDefinitionExample
Angular Velocity (ω)The rate at which an object rotates or revolves about an axis, typically measured in radians per unit of time (e.g., radians per second).A wheel spinning at 2π radians per second completes one full revolution every second.
RadianA unit of angle measure based on the radius of a circle. One radian is the angle created when the arc length is equal to the radius. 2π radians = 360°.An angle of π/2 radians is equivalent to a 90° right angle.
Sector of a CircleThe portion of a circle enclosed by two radii and the arc between them, resembling a slice of pizza.A 90° (or π/2 radian) sector of a circle with radius 4 covers one-quarter of the circle's area.
Gear RatioA ratio that describes the relationship between the rotational speeds of two or more con...
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Core Formulas
Total Angular Displacement
\Delta\theta = \omega \times t \times n
Used to find the total angle (Δθ) an object rotates through. Multiply the angular velocity (ω) by the time (t) and any other multiplicative factors (n), such as the number of identical objects or cycles.
Total Area of Multiple Sectors
A_{total} = n \times (\frac{1}{2} r^2 \theta) \times c
Used to find the total area covered by sectors. Multiply the number of sectors (n) by the area of a single sector ( (1/2)r²θ ) and the number of cycles or repetitions (c).
Magnitude of Product of Complex Numbers
|z_1 \cdot z_2 \cdot z_3| = |z_1| \cdot |z_2| \cdot |z_3| = r_1 \cdot r_2 \cdot r_3
When multiplying three or more complex numbers in polar form, the magnitude of the resulting complex number is the product o...
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Challenging
A robotic painter is programmed to paint 12 identical sectors on a circular canvas of radius 2 meters. The angle of each sector is 15°. The process requires 3 coats of paint. If the special paint costs $50 per square meter, what is the total cost of the paint required for the entire job?
A.$300π
B.$150π
C.$600π
D.$1200
Challenging
A motor provides an initial angular velocity of 100 rad/s. It passes through a 5:1 gear reduction. Then it passes through a second 4:1 gear reduction. However, each gear reduction stage is only 90% efficient, meaning the output velocity is 90% of the ideal calculated value. The system runs for 2 seconds. What is the final angular displacement of the output shaft?
A.10 radians
B.8.1 radians
C.9 radians
D.4.05 radians
Challenging
A point z₀ in the complex plane with magnitude 2 undergoes a sequence of 3 transformations. Each transformation Tₖ scales the existing magnitude by a factor of 3/2. What is the magnitude of the point after all three transformations?
A.4.5
B.6.0
C.6.75
D.8.0
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