Coded letter sums

The idea

In these questions, letters stand for numbers: you are told things like A = 8 and D = 3. A sum is written in letters, and you must work it out and give the answer back as a letter.

There are three moves. First, swap every letter in the sum for its number. Second, work out the sum in numbers. Third — the step everyone forgets — swap the number answer back into the letter that stands for it.

The letters are not in alphabet order and their values are not their alphabet positions; A = 8 means the code says so, not that A is the eighth letter. Use only the code you are given, and check the number answer appears in the code before you swap it back.

Worked example

In a code, A = 8, D = 3, G = 5, F = 2, B = 4. Using the code, work out G − D. Give your answer in the code.

1. Swap the letters for numbers: G = 5 and D = 3.
2. Work out the sum: 5 − 3 = 2.
3. Swap back: the letter that stands for 2 is F.

Answer: F

Watch out

• Giving the number as the answer instead of swapping it back into a letter.
• Reading the code values as alphabet positions (A = 1, B = 2) instead of using the given code.
• Swapping only the first letter and trying to calculate with the rest still as letters.