In a certain code language, each letter is assigned a unique digit. Based on the given codes for specific words, determine the code for the target word using the same logic. If MOUSE is coded as 45291 and RAT as 786, how is STORE coded?

Correct — A.
Rule: each letter keeps one fixed digit, in the word's own order.

MOUSE = 45291 → M4, O5, U2, S9, E1.
RAT = 786 → R7, A8, T6.

STORE → S9, T6, O5, R7, E1 = 96571 → option (a).

Why the others are wrong

• (b)
  97653 — 97653 keeps S = 9, then goes wrong at the second digit: T is 6, not 7 (7 is R). Its last digit, 3, belongs to no letter in MOUSE or RAT.
• (c)
  98345 — 98345 gives T the 8 that belongs to A, and O the unused digit 3. Only the first digit, S = 9, is right.
• (d)
  96278 — 96278 gets S, T and R right (9, 6, 7), but gives O the 2 that belongs to U and E the 8 that belongs to A. O is 5 and E is 1.

This is a letter-to-digit substitution. Every letter has one fixed digit, and the code keeps the letters in the word's order. Write the two given words out as a key, M4 O5 U2 S9 E1 R7 A8 T6, and read the new word off it letter by letter.

STORE uses only letters already present in MOUSE and RAT, so nothing has to be guessed.

Key facts

• MOUSE = 45291 and RAT = 786 give eight letters eight different digits.
• No given letter carries 0 or 3, so an option containing either is wrong for STORE.
• STORE = S9 T6 O5 R7 E1 = 96571.

Common traps

• Taking the digit of a neighbouring letter, such as A's 8 for T
• Choosing an option because its first digit matches, without checking the rest

No directly related past PYQ was found.