Opposite letters add to 27

Learning outcome

You can code a word by replacing each letter with the letter that completes 27.

Concepts and reasons

Opposite letters come in pairs whose places add to 27. A is 1 and pairs with Z, which is 26. B is 2 and pairs with Y, which is 25. C is 3 and pairs with X, which is 24. The middle pair is M and N, because 13 + 14 = 27.

To code a word, replace every letter by its opposite. Do not also reverse the word unless the question says so. CAT becomes XZG: C pairs with X, A with Z, and T, which is 20, pairs with G, which is 7, because 20 + 7 = 27.

Worked examples

1. Opposite of CAT is XZG.
2. Opposite of DOG is WLT. D is 4 and pairs with W, 23. O is 15 and pairs with L, 12. G is 7 and pairs with T, 20.
3. Opposite of BLACK is YOZXP. B-Y, L-O, A-Z, C-X, K-P. Check one sum: K is 11 and P is 16, and 11 + 16 = 27.

Common traps

A shift of +1 is not an opposite. CAT shifted by +1 is DBU, not XZG. Do not use 26 as the sum. A plus Z is 1 + 26 = 27, not 26. Reversing the opposites is a second step. This lesson stops at the opposite letter in the same order.

Practice questions

1. What is the opposite code of PEN?
2. What is the opposite code of SUN?
3. Which pair does not sum to 27: A-Z, B-Y, C-W, D-W?

Answers and explanations

1. KVM. P is 16 and pairs with K, 11. E is 5 and pairs with V, 22. N is 14 and pairs with M, 13.
2. HFM. S is 19 and pairs with H, 8. U is 21 and pairs with F, 6. N is 14 and pairs with M, 13.
3. C-W. C is 3 and W is 23, and 3 + 23 = 26, not 27. The opposite of C is X. D-W is a true pair, because 4 + 23 = 27.

Analogy

The alphabet folded in half meets in the middle. The first letter meets the last, the second meets the second last, and each pair adds to 27.

Quick reference

• Places add to 27, not 26.
• A-Z, B-Y, C-X, D-W, E-V, F-U, G-T, H-S, I-R, J-Q, K-P, L-O, M-N.
• CAT becomes XZG. DOG becomes WLT.
• Keep the letter order. Reversing is a different instruction.