Mirror and water images, worked through

A mirror image is what you see with a mirror stood upright to the right of a word (or to its left — the answer is the same). Left and right swap; top and bottom do not. The word reads backwards, and each letter is reversed in place.

A water image is the reflection in water lying below the word. Top and bottom swap; left and right do not. The letters stay in their order, and each one is upside down. Doing both — mirror, then water — turns the word half way round, which is a different answer again and a favourite wrong option.

Questions are built on the letters that survive a reflection, because they are the ones that make two options look alike. In plain capitals:

• Unchanged in a mirror (symmetric about an upright line): A, H, I, M, O, T, U, V, W, X, Y, and the digits 0 and 8.
• Unchanged in water (symmetric about a level line): B, C, D, E, H, I, K, O, X, and 0, 3 and 8.
• Unchanged in both (a half turn): H, I, N, O, S, X, Z, and 0 and 8.

The lists belong to the typeface, not the alphabet. A serif on one foot of an A, a spur on a G or a slanted italic breaks the symmetry, which is why exam papers print the question in plain capitals. Lower case is far less reliable: b and d swap in a mirror, p and q swap too, and b and p swap in water.

Mirror image of TOMATO. Every letter — T, O, M, A — is symmetric about an upright line, so each one looks the same in the mirror; only the order reverses. TOMATO read backwards is OTAMOT, and that is exactly what the mirror shows. An option that shows TOMATO unchanged is wrong — that would need a palindrome.

Water image of CODE. C, O, D and E are each symmetric about a level line, and a water image keeps the order. So the water image of CODE looks exactly like CODE. A question built on it is testing whether you know the order does not reverse.

Mirror image of a clock at 3:40. The mirror swaps left and right, so the hands point to 12:00 minus the time: 12:00 − 3:40 = 8:20. The quick rule works for any time on an analogue clock with no numbers; check it by looking at where the hour hand sits between the marks.

Water image of 3:40. Water swaps top and bottom, so the reading is 18:30 minus the time: 18:30 − 3:40 = 14:50, which a twelve-hour clock shows as 2:50. Different rule, different answer — the reason papers set both.

The mirror text tool on this site sets any word in a plain sans serif, draws its mirror and water images, and highlights the letters that stay the same. Its practice panel asks the same kind of question with four drawn options — the right reflection, the other reflection, the half turn and the letters merely written backwards — and explains the answer. It is a practice aid. Mirror and water images appear in SSC CGL reasoning papers according to commonly cited syllabus summaries; check the notice for the exam you are taking.