Solution to the chocalate math problem
Here is a puzzle that will
always jinx you.
Follow these steps.
Pick a number ______
multiply by 6 ______
subtract 3 ______
divide by 3 ______
Add 5 ______
Divide by 2 ______
Subtract the original number ______
Try it with three different numbers.
Do you think it will always work? Why do
you think that?
To see if it always works, make a spreadsheet
model of this puzzle.
Open Appleworks (or Excel)
Type in the text as you see it above.
Enter the formula =D3 + 11 in cell D4
Enter the formula =D4 * 6 in cell D5.
Continue until you have entered the formulas
for cells D6 through D10.
After you finish entering the formulas, enter
a numeric value in D3, like 6.
Look at cell D10. Does it show 13? (If not,
check your formula in D10.)
Did D10 show 13? Try a different number in D3.
Did you get 13 in cell D10? Well, that means
your number (6 in this case) jinxed you. You got 13 - the unlucky number!
Make 3 additional columns.
Highlight D3 through G10. (It forms a rectangle.)
Choose Fill Right from the Calculate menu.
Next enter different numbers in D3, E3, F3,
G3 so it looks something like this. Try your own numbers.
Can you find a number that will not always
end up as 13?
If not, why not?
4.1 (B) Birthday Puzzle
Create the birthday problem
spreadsheet for the puzzle below. See if you can figure out what has to
be done in order to figure out how this "mind reading" trick works.
Here is the information the
"magician" asks for
Ask the participants to write
down the number of the month of the year in which they were born.
Write the number of the day they
Have them do the calculations
Ask a participant what number
they got. From that number the Math Magician hears, he or she can determine
the personís birthday. See if you can figure out what he does.
Build the spreadsheet. Collect
some data. From the data see if you can figure out whatís going on.. Add
one more row to the spreadsheet called "the secret formula" so that the
birthday is revealed.
Month of Birthday
The number of the day of birthday
Multiply month by 5
Multiply by 4
Multiply by 5
Add the day of the month
Hint: If your birthday is on November
5th the number you should get from the spreadsheet is 1310. How can you
find the date of your birthday from that number? (Hint Your birthday is
1105 so what if you subtracted 205 from 1310?)
Back to problem page