Sunday 6 January 2013

Reverse Cipher Puzzle - Part 2

Looking at the formulae, you can see that in the subtraction we have, in the rightmost column, S - S = R, so R = 0 (zero). Going to the complex formula, you can see that subtracting O from TO gives a multiple of 10, so ignoring whatever T might be for the moment, (E + S) = 10. If you look at the addition, in the rightmost column, (S + O) = U (+ 10) (that is possibly 10). In the next column we have E + S, which we know is 10, so J is either zero or 1. It can't be zero because that's R, so it must be 1.

12345 67890
J R

Looking at the subtraction again, we've got another formula, (E - S) = T, the second column from the right. Using what we already know about E and S, we can say:

E - S = T
E - (10 - E) = T
2E - 10 = T
2E = T + 10
E = (T + 10) / 2

So for E to be a whole number, and a single digit, T must be even.

TES
264
473
682
891

T can't be 8 as S can't be 1 (it's J). In the subtraction, the third column from the right has T + E + 1 = U (+ 10), the 1 being carried over from (E + S). Plugging this into the table we get:

TESU
2649
47312 (or 2 + 10)
68215 (or 5 + 10)

Remember the first formula, (S + O) = U + 10, we got from the subtraction? We substitute 10 = (E + S) as before:

S + O = U + 10
S + O = U + S + E
(removing S each side)
O = U + E

Using this to get values for O:

TESUO
2649(6 + 9) = 15
4732(2 + 7) = 9
6825(5 + 8) = 13

O must be a single digit, so it can't be 15 or 13, leaving us with:

12345 67890
JUST EOR

Putting what we know into the addition, we get 374473 + 73F739 = 1113212 and making the obvious subtraction, 1113212 - 374473 = 738739, gives F = 8, leaving C and I.

Doing the same to the subtraction, 74873 - IC233 = 18C40, the third column from the right, 8 - 2 = 6, so C = 6 and I is 5:

12345 67890
JUSTI CEFOR

Which makes our formulae:

47737 * 65 = 3102905 374473 + 738739 = 1113212
74873 - 56233 = 18640 ((7 + 3) * 4) + 9 = 49

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