Imagine you are a carpenter and you are tasked with laying wooden floor at Gill Bates’ house. Now Gill B has a very big house and he wants to make sure you do a good job. So instead of asking you to lay the floor for entire house, he asks you to finish flooring in the guest bedroom first. Here are the dimensions of that guest bedroom.
- Width: 6ft 3inches
- Length: 24ft 9inches
- Size of individual wooden floor board: 2ft x 4inches
And here is the big question you are facing.
What?!? the guest bedroom width is only 6ft 3inches?
But over the years of chiseling and polishing you have learned to keep quiet and do your work.
So the real question you have is, How many wooden floor boards should you buy?
Of course, you want to find the answer using Excel. Why else would a carpenter read this blog?
Multiplying Feet & Inches using Excel
If the metric system became an universal standard for measuring things, we all can stop worrying and go to that wooden tile store to place order now. Alas, we still have to deal with feet, inches, miles, pounds, ounces and gallons (not to mention irrational numbers like pi, e and eleventeen).
Fortunately, Excel has 2 powerful features to support calculations like this.
Method 1: Using CONVERT()
CONVERT() as the name suggests is an Excel function that can convert values from one base to another, like feet to inches, square meters to square feet, centigrade to fahrenheit, grape juice to wine. Well, not the last one, but it shines in all other scenarios.
So we can use CONVERT() to first convert all the numbers to a common base like meters or inches or feet. Then perform the arithmetic. Once done, convert back to Feet & Inches.
Pretty simple eh?
See this model:
The process is simple:
- First we convert all feet & inch values to meters
- This is done with =CONVERT( feet value + inch value / 12, “ft”, “m”)
- Once we have values in meters, we perform the arithmetic by simple multiplication & division.
Method 2: Using Fraction Cell Format
If you don’t feel so hot for the CONVERT(), then this method works for you. You can use fraction cell formatting to enter fractions like 6 3/12 and 24 9/12 in to cells and let Excel treat them as regular numbers when multiplying, adding or dividing.
See this model:
How to set it up?
- Select all the cells where you need values to be shown in feet inches fraction format
- Press CTRL + 1 (or right click and format cells)
- Select Custom and enter the formatting code as
- # ??/12
- This ensures that when you type a fraction like 6 3/12, Excel treats that as number (6.25)
- Rest of the arithmetic is simple.
Related: Custom Cell Formatting in Excel – Tips, more tips, even more tips
Bonus Tricks
Here are few more scenarios where you can use either CONVERT() or fraction formatting.
- If varnishing 1 square feet takes 2 minutes 30 seconds, how much times does it take to finish a 20 ft 6 in x 12 ft 9 in room?
- If average customer call lasts 3 minutes 10 seconds and Cynthia took 400 calls in last week, how many hours did she work?
- If Mr. Gill Bates earns $1000 per every 1 minute 4 seconds, how many days does it take for him to earn $10 million?
- How many teaspoons of honey per gallon?
Download example workbook:
Click here to download example workbook. It shows 3 methods for solving this problem. Examine the formulas and format settings to learn more.
Do you use Excel for these kind of problems?
I am not much of a carpenter. Few years ago, I decided to add a door to my office desk so that my kids (they learned how to crawl around that time) wouldn’t poke the reset button of my CPU. After buying necessary material (a wooden plank, nails, hinges, magnetic door locks) and wasting a day hammering nails in to my fingers, bending one of the hinges, almost breaking the wooden plank in to two, I gave up and closed the shelf-space completely instead (here is a pic of my carpentering disaster). So it suffices to say I do not use Excel for modeling my carpentry jobs.
But I am sure many of our readers are better carpenters, masons, plumbers, knitters or cooks than me. So tell me. Do you use Excel for modeling these kind of problems? What formulas, techniques and tips do you use? Please share using comments.
Now if you excuse me, I have to go look at the leaky faucet my wife is complaining about. I am sure I can ruin it with a pipe wrench.
14 Responses to “How many ‘Friday the 13th’s are in this year? [Formula fun + challenge]”
in C3=2016
in C4=3
in C5=1 (the first next year with three Friday the 13ths)
=SMALL(IF(MMULT(--(MOD(DATE(C3+ROW(1:1000),COLUMN(A:L),13),7)=6),ROW(1:12)^0)=C4,C3+ROW(1:1000)),C5)
formula check in the next 1000 years
This will generate a table of counts of Friday the 13th's by year. If I didn't screw it up the next year with three is 2026.
I created a simple parameter table with a start date and end date that I wanted to evaluate. That calculates the number of days and generates a list of those days. Then filter and group. The generation of the list in power query (i.e. without populating a date table in excel) is pretty cool, otherwise this isn't really doing anything than creating a big date and filtering/counting.
let
Source = List.Dates(StartDateAsDate, Days2, #duration(1,0,0,0)),
ConvertDateListToTable = Table.FromList(Source, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
AddDayOfMonthColumn = Table.AddColumn(ConvertDateListToTable, "DayOfMonth", each Date.Day([Column1])),
AddYearColumn = Table.AddColumn(AddDayOfMonthColumn, "Year", each Date.Year([Column1])),
AddDayOfWeekColumn = Table.AddColumn(AddYearColumn, "Day of Week", each Date.DayOfWeek([Column1])),
FilterFriday13 = Table.SelectRows(AddDayOfWeekColumn, each ([DayOfMonth] = 13) and ([Day of Week] = 5)),
Friday13thsByYear = Table.Group(FilterFriday13, {"Year"}, {{"Number of Friday the 13ths!", each Table.RowCount(_), type number}})
in
Friday13thsByYear
With the parameters replaced by values should you want to play along at home. This runs for 20 years starting on 1/1/2016.
let
Source = List.Dates(#date(2016,1,1), 7300, #duration(1,0,0,0)),
ConvertDateListToTable = Table.FromList(Source, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
AddDayOfMonthColumn = Table.AddColumn(ConvertDateListToTable, "DayOfMonth", each Date.Day([Column1])),
AddYearColumn = Table.AddColumn(AddDayOfMonthColumn, "Year", each Date.Year([Column1])),
AddDayOfWeekColumn = Table.AddColumn(AddYearColumn, "Day of Week", each Date.DayOfWeek([Column1])),
FilterFriday13 = Table.SelectRows(AddDayOfWeekColumn, each ([DayOfMonth] = 13) and ([Day of Week] = 5)),
Friday13thsByYear = Table.Group(FilterFriday13, {"Year"}, {{"Number of Friday the 13ths!", each Table.RowCount(_), type number}})
in
Friday13thsByYear
=MATCH(3,MMULT(N(WEEKDAY(DATE(C3+ROW(1:100)-1,COLUMN(A:L),13))=6),1^ROW(1:12)),)+C3-1
It should be pointed out that Alex's solution, unlike some others, has the additional advantage of being non-array. My solution was nearly identical but with -- and SIGN instead of N and 1^.
=C3-1+MATCH(3,MMULT(--(WEEKDAY(DATE(C3-1+ROW(1:25),COLUMN(A:L),13))=6),SIGN(ROW(1:12))),0)
Sub Friday13()
Dim StartDate As Date
Dim EndDate As Date
Dim x As Long
Dim r As Long
Range("C7:C12").ClearContents
StartDate = CDate("01/01/" & Range("C3"))
EndDate = CDate("31/12/" & Range("C3"))
r = 7
For x = StartDate To EndDate
If Day(x) = 13 And Weekday(x, vbMonday) = 5 Then
Cells(r, 3) = Month(x)
r = r + 1
End If
Next
End Sub
Calculate next year with 3 Friday 13th. Good for 100 years different from year entered in cell C3
Sub ThreeFriday13()
Dim StartDate As Date
Dim EndDate As Date
Dim x As Long
Dim WhatYear As Integer
Dim Counter As Integer
Range("E7").ClearContents
StartDate = CDate("01/01/" & Range("C3") + 1)
EndDate = CDate("31/12/" & Range("C3") + 100)
Counter = 0
For x = StartDate To EndDate
If WhatYear Year(x) Then
WhatYear = Year(x)
'Different year so reset counter
Counter = 0
End If
If Day(x) = 13 And Weekday(x, vbMonday) = 5 Then
Counter = Counter + 1
If Counter = 3 Then
WhatYear = Year(x)
Exit For
End If
End If
Next
Range("E7") = WhatYear
End Sub
*RE-POST as not equal did not show earliuer
Calculate next year with 3 Friday 13th. Good for 100 years different from year entered in cell C3
Sub ThreeFriday13()
Dim StartDate As Date
Dim EndDate As Date
Dim x As Long
Dim WhatYear As Integer
Dim Counter As Integer
Range("E7").ClearContents
StartDate = CDate("01/01/" & Range("C3") + 1)
EndDate = CDate("31/12/" & Range("C3") + 100)
Counter = 0
For x = StartDate To EndDate
If WhatYear NE Year(x) Then
WhatYear = Year(x)
'Different year so reset counter
Counter = 0
End If
If Day(x) = 13 And Weekday(x, vbMonday) = 5 Then
Counter = Counter + 1
If Counter = 3 Then
WhatYear = Year(x)
Exit For
End If
End If
Next
Range("E7") = WhatYear
End Sub
earlier*
I've a doubt with using array formula here.
In sample workbook, I tried to replicate the formula again.
=IFERROR(SMALL(IF(WEEKDAY(DATE($C$3,ROW($A$1:$A$12),13))=6,ROW($A$1:$A$12)),$B7),"")
For this I selected C7 to C12, and typed the same formula and pressed ctrl+alt+Enter. But in all cells it is taking $B7 (and not $B7, $B8, $B9.... etc)
and since it is array formula I can't edit individual cell.
Please guide.
Thanks
Hi Chandoo,
Cool stuff. You need to clarify that the answer of 5 represents the 1st month in the year that has a Friday the 13th, and not the number of Fridays the 13th in the year. Subtle, but important difference.
Thanks,
Pablo
I like the MMULT() function far more, but here's how I would have tackled it. It uses an EDATE() base and MODE() over 100 years. I'm assuming that 100 years is enough time to catch the next year with 3 friday 13th's. Array entered, of course.
{=MODE(IFERROR(YEAR(IF((WEEKDAY(EDATE(DATE(C3, 1, 13), ROW(INDIRECT("1:1200"))))=6), EDATE(DATE(C3, 1, 13), ROW(INDIRECT("1:1200"))), "")), ""))}
Finding all the Friday the 13ths in a Year:
=SUMPRODUCT((DAY(ROW(INDIRECT(DATE(C3,1,1)&":"&DATE(C3,12,31))))=13)*(TEXT(ROW(INDIRECT(DATE(C3,1,1)&":"&DATE(C3,12,31))),"ddd")="Fri"))
{=sum(if(day.of.week(DATe($YEAR;{1;2;3;4;5;6;7;8;9;10;11;12};13);1)=6;1;0))}
just list the years