Practice Questions - Process Analysis with Key Metrics
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Boston College *
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Course
1021
Subject
Industrial Engineering
Date
Dec 6, 2023
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Pages
8
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1
PROCESS ANALYSIS WITH KEY METRICS
List of Key Topics
• Process Flowcharts and Its Elements
• Process Flow Measures: Inventory, Flow Time, Flow Rate (Throughput)
• Little’s Law
Notation
I
Inventory
R
Throughput (Flow Rate)
T
Flow Time
Formulas
Little’s Law
I = R * T
2
PRACTICE QUESTIONS
A. Determine whether the following statements are true or false. Explain your reasoning in 1-
2 sentences for false statements.
• Little's Law can be used to identify the actual time a particular flow unit spends in a process.
True | False
• Suppose that flow time at a company increases. If the company needs to keep the same level
of throughput, it needs to increase its inventory level.
True | False
• If a business is willing to delay production closer to the time of sales to gain valuable market
information, then it should aim to increase its flow time.
True | False
•
Outsourcing some part of a business process to a 3
rd
-party company increases the complexity
level of process flowcharts.
True | False
• If a process flowchart has a decision point, flow units might not go through all the activities and
buffers.
True | False
B. Answer the following questions and state your assumptions if you make any.
Q
1
.
At rush hour, 2 people per second step onto an escalator. The escalator takes 30 seconds to
bring a person from bottom to the end. If we would like to know how many people are on the
escalator, which measure are we looking for?
A)
Inventory
B)
Flow Rate
C)
Flow Time
3
Q
2
.
On average, a patient spends 5 minutes waiting and 15 minutes being treated at a clinic. The
average number of patients waiting and being treated at the clinic is 50. What is the average flow
rate of patients per minute on a typical day?
Q
3
.
Lucy works in a candy factory wrapping individual chocolate truffles in a candy wrapper. The
factory makes 500 truffles each hour and, at any given time, there are 75 truffles currently being
made. How long does it take for Lucy to wrap each truffle?
Q
4
.
A drive-through at a fast-food franchise serves 300 customers over a 10-hour day. On
average, a customer spends 2 minutes waiting in line, 3 minutes placing the order, and 5 minutes
completing the order before leaving the drive-through. How many customers on average are "in"
the drive-through (i.e., from the time they enter to the time they exit the drive-through) on a
typical day?
Q
5
.
Assume a stable process.
Both the average flow rate and average flow time of a process are
increased by 50%. What will be the percentage change in the average number of units in the
process?
A)
225%,
B)
125%,
C)
50%, or
D)
25%? Show/Explain your work briefly.
Q
6
.
A furniture maker purchases 1200 kgs of wood per week to make chairs. Each chair uses 25
kgs of wood. At any time on average, there are 300 chairs being made. How long does it take to
make a chair?
A)
0.16 weeks
B)
4 weeks
C)
6.25 weeks
D)
12 weeks
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4
Q
7
.
The process in a typical call center starts with an incoming call from a customer and this goes
into a voice response unit (VRU) that is designed with some ability to understand the issues that
customers report and provide automatic answers. In this process, first the VRU requests caller
information. If the VRU can understand this information, it gets the description of the issue from
the caller and evaluates whether it can be resolved without a customer representative. If it can
be resolved, then the VRU handles the issue and ends the call after getting feedback from the
caller. If it cannot be resolved, then it refers the caller to a customer representative. If the VRU
cannot understand the caller in the first place, it refers it to a customer representative as well. If
the representative cannot address the issue based on his/her knowledge, then he/she transfers
the call to a subject matter expert. Both the representative and subject matter expert transfer
the call to the VRU at the end for the caller to provide feedback at the end.
Draw a flowchart for this call center process assuming unlimited lines for the VRU and limited
number of representatives and subject experts.
5
Q
8
.
Employees at Peet’s Coffee & Tea in Brookline, MA have conducted a time study for the
busiest time period during the day and found that during that time it takes 2 minutes for them
to get a single customer’s order on average. They have also observed that on average there are
8 customers waiting to order, 1 customer at the cashier, and 5 customers are waiting to receive
their order. Answer the following questions for the busiest time period. (
Note:
You can assume
that receiving the order is instantaneous.)
A.
Draw a process flowchart for the process described above.
B.
What is the arrival rate of customers?
Q
9
.
A.
There is a food service process that takes on average 20 minutes to complete the service
of a customer and there are 12 people arriving every hour. On average, how many people are
being served?
B.
Now we know the service process takes on average 10 minutes to complete and there are on
average 5 people being served. How many per hour are arriving?
6
Q
10
.
For the new Euro introduction in 2002, Wim Duisenberg, President of the European Central
Bank, had to decide how many new Euro coins to stamp by 2002. Euroland’s central banks’ cash-
in-coins handling was estimated at €300 billion per year. The average cash-in-coins holding time
by consumers and businesses was estimated at 2 months. How many Euro coins were to be
made?
Q
11
.
A.
A wholesaler sells $300 million worth of clothes and accessories to retailers per year. The
average accounts receivable is $45 million. What is the average billing-to-collection process cycle
time? Assume a year has 52 weeks.
B.
If the average billing-to-collection process cycle time is cut to 5 weeks, how would that affect
the average accounts receivable?
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7
Q
12
.
The Evanstonian is an upscale independent hotel that caters to both business and leisure
travelers. On average, one-third of the guests checking in each day are leisure travelers. Leisure
travelers generally stay for 3.6 nights – twice as long as the average business customer.
A.
On an average day, 135 guests check into the Evanstonian. On average, how many guests of
each type are in the hotel at any given day?
B.
The average business traveler pays a rate of $250 per night, while leisure travelers pay an
average rate of $210 per night. What is the average revenue The Evanstonian receives per night
per occupied room?
Q
13
.
A college cafeteria has three types of checkout lanes: cashier service for students paying
with cash, cashier service for students paying with a credit card, and self- service for students on
the meal plan who are paying with their student IDs. The paragraph below provides a detailed
process description. Associated process flowchart (together with given analysis metrics) are
provided in the figure below.
Overall, an average of 5 students/minute arrive at the cafeteria. Assuming a stable process,
answer the questions below.
8
A.
How many students are there in the food court area of the cafeteria (excluding the checkout
area) and what is average time spent in this area?
B.
The manager of the cafeteria would like customers to get though the credit-card lane faster.
Which change in the process would result in the greatest reduction in average flow time for
customers using credit cards?
Choose (i) or (ii) and show supporting calculations. Assume there are no changes in other values
given.
(i) an increase in the percentage of students paying with the credit card from 30% to 40%
(ii) a reduction of 2 customers in the waiting line for the credit card check-out (from 10 to 8)
RECOMMENDED PROBLEMS FROM TEXTBOOK
Chapter 2. Conceptual Questions
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Chapter 2. Problems/Applications
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