Question

Difficulty: Very hardSimultaneous Equations and Systems

A semiconductor manufacturing facility operates two models of photolithography equipment: Model D and Model E. Over a 10-hour operational cycle, each Model D scanner consumes 400 kWh400\text{ kWh} of energy and processes 600600 silicon wafers, while each Model E scanner consumes 1,200 kWh1,200\text{ kWh} of energy and processes 1,0001,000 silicon wafers. If the combined fleet consumed a total of 9,600 kWh9,600\text{ kWh} of energy and processed 10,40010,400 wafers over the cycle, which of the following correctly identifies the number of Model D scanners and Model E scanners operated by the facility?

  1. 9 Model D scanners and 5 Model E scannersAnswer
  2. B
    5 Model D scanners and 9 Model E scanners
  3. C
    12 Model D scanners and 4 Model E scanners
  4. D
    6 Model D scanners and 6 Model E scanners
  5. E
    15 Model D scanners and 3 Model E scanners

Answer

9 Model D scanners and 5 Model E scanners
The correct answer states 9 Model D scanners and 5 Model E scanners. Setting up the system d+3e=24d + 3e = 24 (energy) and 3d+5e=523d + 5e = 52 (production) and solving by substitution gives e=5e = 5 and d=9d = 9, which uniquely satisfies both constraints.

Step-by-Step Solution

1
Define variables and establish equations based on given rates and totals.
Let dd be the number of Model D scanners and ee be the number of Model E scanners.
Energy equation: 400d+1200e=9600400d + 1200e = 9600
Wafer equation: 600d+1000e=10400600d + 1000e = 10400
Translate the physical constraints into a system of two linear equations.
2
Simplify both linear equations by dividing by their greatest common divisors.
Dividing the energy equation by 400400 gives:
d+3e=24— (Equation 1)d + 3e = 24 \quad \text{--- (Equation 1)}
Dividing the wafer equation by 200200 gives:
3d+5e=52— (Equation 2)3d + 5e = 52 \quad \text{--- (Equation 2)}
Simplifying constants reduces calculation complexity and prevents arithmetic errors.
3
Solve the system using substitution or elimination.
From Equation 1, express dd in terms of ee:
d=243ed = 24 - 3e
Substitute this expression into Equation 2:
3(243e)+5e=523(24 - 3e) + 5e = 52
729e+5e=5272 - 9e + 5e = 52
724e=5272 - 4e = 52
4e=20    e=54e = 20 \implies e = 5
Now calculate dd:
d=243(5)=2415=9d = 24 - 3(5) = 24 - 15 = 9
Isolating one variable yields exact values for both equipment models.
4
Verify values against both constraints.
Energy: 400(9)+1200(5)=3600+6000=9600 kWh400(9) + 1200(5) = 3600 + 6000 = 9600\text{ kWh}
Wafers: 600(9)+1000(5)=5400+5000=10400 wafers600(9) + 1000(5) = 5400 + 5000 = 10400\text{ wafers}
Ensures the solution satisfies both independent constraints simultaneously.

Key Concept

Simultaneous Linear Equations in Two Variables
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