# SOLUTION to Challenge 7: A Simple Substitution Congratulations to Bill Briere and Euchre Mutt for solving Challenge 7 on September 22. It took them less than a day! Bill Briere was the first to send me the correct solution. Euchre Mutt sent me his a few hours later. I would normally only assign points to the first solver, but because the answers were sent so close to each other, I will assign points to each. Since this puzzle took less than a day to solve, each guesser gets one point.

I’ll reveal the secrets below, but if you haven’t tried your hand at solving it, read this first.

The solution is after the jump.

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Ciphertext:

X K W L Y N L A N X
T Z R T X W L J X M
V J A U H T I V K I
X O N V I O C A J V
X S Y L A Y V N X Z
R C B N O D J V O Q
A K Y K A I B R V J
P B V P P M D V F T
L W B X P B C O Y R
V P D D R U V C

Plaintext:

W I T H T H E S E N
I N E F I G U R E S
A N D W I T H T H E
S I G N Z E R O W H
I C H T H E A R A B
S C A L L Z E P H I
R A N Y N U M B E R
W H A T S O E V E R
I S W R I T T E N F
I B O N A C C I

Formatted:

“With these nine figures and with the sign zero, which the Arabs call ‘zephir,’ any number whatsoever is written. — Fibonacci”

The quote is from Fibonacci’s seminal math book Liber Abaci, the book that introduced Hindu-Arabic numbers to the West.  What are Hindu-Arabic numbers? “0-9,” the very same numbers we use today! Fibonacci’s real name was Leonardo of Pisa, which explains why I used the close-up of the Leaning Tower of Pisa in the challenge image.

To decipher, all you need to do is convert the letters to numbers, where A=1, B=2, etc. Then, subtract the position of the number from that number. For example, since X is in the first position, you would subtract 1 to get W. Since K is in the second position, you would subtract 2 to get I. Subtract 3 from third position, 4 from fourth, etc. If the resulting number is negative, add 26. Since there are 26 letters in the alphabet, after position 26, start at 1 again.

I made a typo in my original version, which caused both solvers to write “figures” as “fygures.” I have since corrected my error.