In a certain code GALIB is represented by HBMJC. TIGER will be represented by

Concept — In a letter-coding problem the code word is built from the original word position by position: the first letter of the word gives the first letter of the code, the second gives the second, and so on. To fix the rule, measure the alphabetical shift at each place, that is, the position number of the code letter minus the position number of the original letter. When the same shift repeats at every place, that constant shift is the code.

Application — Compare GALIB with HBMJC, letter by letter.

The shift is +1 at every place, so the rule is: replace each letter by the letter that comes next in the alphabet, and keep the letters in their original order.

Now apply the same rule to TIGER.

1. T is the 20th letter of the alphabet, so it becomes U, the 21st letter.

2. I is the 9th letter of the alphabet, so it becomes J, the 10th letter.

3. G is the 7th letter of the alphabet, so it becomes H, the 8th letter.

4. E is the 5th letter of the alphabet, so it becomes F, the 6th letter.

5. R is the 18th letter of the alphabet, so it becomes S, the 19th letter.

Reading the five code letters in the same order as the letters of TIGER gives UJHFS.

Cross-check — Applying the reverse rule to UJHFS turns U back into T, J into I, H into G, F into E and S into R, which restores TIGER, so the rule works in both directions. Order matters too: UHJSF, JHUSF and HUJSF are made of the same five letters, but they do not place those letters where the next-letter rule puts them.