Explanation
In the word PREMIUM, the positions and alphabetical numerical values of the letters are P (position 1, value 16), R (position 2, value 18), E (position 3, value 5), M (position 4, value 13), I (position 5, value 9), U (position 6, value 21), and M (position 7, value 13).
Checking pairs in both forward and backward directions yields three valid pairs:
First, the pair P and U in the forward direction. P is at position 1 and U is at position 6, giving a positional difference of 6 − 1 = 5. In the English alphabet, the difference between P (16) and U (21) is also 21 − 16 = 5.
Second, the pair M and P in the backward direction. M at position 4 and P at position 1 have a positional difference of 4 − 1 = 3. In the alphabet, the difference between M (13) and P (16) is also 16 − 13 = 3.
Third, the pair M and R in the backward direction. M at position 7 and R at position 2 have a positional difference of 7 − 2 = 5. In the alphabet, the difference between M (13) and R (18) is also 18 − 13 = 5.
Therefore, there are 3 such pairs of letters in total.