Wentworth Institute of Technology
Division of Professional and Continuing Studies
COMP112 Section 71 – Introduction to Computers and Programming – Spring,2009
Homework 7 – Excel Problem – Time To Recoup Expense
Instructor: Bob Goldstein (617) 912-2512
bobg@vision.eri.harvard.edu
robert.goldstein@schepens.harvard.edu
http://home.comcast.net/~goldsteinr/Courses/index.html
http://goldstein.eri.harvard.edu/courses/index.html
http://myweb.wit.edu/goldsteinr/Courses/index.html
Due Date: April 21, 2009
EMAILyour Excel Worksheet as an attachment
Purpose:
This homework is to exercise your skills in formulating a problem and converting it to an Excel Worksheet.
Description:
(Reference: This homework is based on Hanly and Koffman, Page 92, Problem 5.)
Due to a drought, a community needs to convince homeowners to replace their old toilets with modern ones that use
less water. Unfortunately, it will cost a lot of money to replace the toilets. However, the people who are advocating
for the replacement toilets maintain that the savings in water bills to the residents will quickly make up for the costs
of the new toilets.
Develop an Excel workbook that will calculate the amount of time it will take to recoup the cost to an individual to
replace the toilet in his or her home. Figure out the equations to do this calculation and include them as
documentation as either a separate Word document or on “Sheet2” of your workbook, or in columns to the
right of the working column
Assume that an average household has one toilet, that the average number of people in the household is three people
and that the number of times a person flushes a toilet each day is 4. Assume the existing toilets use an average of 15
liters/flush and the new toilets use only 2 liters/flush. The worksheet should have entry fields for the cost of a new
toilet and the cost/liter of water. BE CAREFUL because the cost of water is in Cents per liter and the cost of a toilet
is in Dollars.
Sample Screen of the Excel Sheet
Time To Recoup Cost of New Tolilet
Cost Per Liter of Water $0.003
Number of people in house 3
Number of flushes per day per person 4
Cost of new toilet (in dollars) $400.00
Number of liters per flush of old toilet 15
Number of liters per flush of new toilet 2
Time to Recoup cost (in days) 854.701
Cost of water per day for old toilet $0.54 This should contain a formula
Cost of water per day of new toilet $0.07 This should contain a formula
Saving per day $0.47
Extra Credit:
Have excel draw a graph that shows the number of days to recoup as a function of the cost of the water. Have
the cost of the water be on the X axis and go from one tenth of a cent per liter to 5 cents per liter.
Extra Extra Credit:
Have the worksheet convert the answer into Years, Months and Days. In other words, the above answer of 854.7
days would display as
PLEASE NOTE - YOU WILL NOT GET EXTRA CREDIT FOR ANY DIRTY JOKES ABOUT THIS
ASSIGNMENT.
/app/work/qkd7yv-353363-2765006-homework7-doc.doc 1 12/5/2020 12/5/2020
Y 2
M 4
D 3.034188