The Digital Clock That Looked Upside Down

Difficulty ★★☆about 4 minEveryday MysteryDigit orientationTime

In a scene photo the digital clock is upside down. The display reads "10:51." What is the real time?

Case Record

In the afternoon, an office worker named Miwa was stabbed to death in a room of a building. A digital clock lay on the floor at the scene.

In the photo taken by the police, the clock appears upside down (rotated 180 degrees), and the display looks like "10:51." The clock has a 7-segment display and had stopped. The police have concluded that it fell to the floor and stopped at the moment of the crime.

Miwa’s phone held a message: "Meet at 15:00."

There are three suspects: Hashimoto, who left the office at exactly 3:00 p.m.; Okada, who left at 2:50 p.m.; and Someya, who left at 3:10 p.m. It is a 5-minute walk from the office to the scene.

Your question

What time does the clock really show, and who could have reached the scene at that time?

Case Files

Evidence

E-1Photo of the clockIt looks upside down. The display reads "10:51."
E-2Phone message"Meet at 15:00."
E-3Three departure timesHashimoto 15:00, Okada 14:50, Someya 15:10. A 5-minute walk from the office to the scene.

Diagram

Timeline

14:50Okada leaves the office.
15:00Hashimoto leaves the office. The agreed meeting time.
15:10Someya leaves the office.

Hints

If you get stuck, open the hints one at a time, in order.

Open hint 1

If you rotate the digits by 180 degrees, how does each one look?

Open hint 2

The order of the digits is also reversed.

Open hint 3

Who could be at the scene at 3:01 p.m.?

Solve It

Your question

What time does the clock really show, and who could have reached the scene at that time?

Choose the answer closest to the truth.

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The Truth

The upside-down 10:51 is 15:01, and Okada could have reached the scene

The answer is: the upside-down 10:51 is 15:01, and Okada could have reached the scene.

The clock fell and stopped at the moment of the crime, so the displayed time is the time of the crime.

On a 7-segment display rotated 180 degrees, 0 stays 0, 1 stays 1 and 5 stays 5, but the order of the digits reverses. Turned upside down, "10:51" becomes "15:01." The real time is 3:01 p.m.

It is a 5-minute walk from the office to the scene. The person who could be at the scene at 3:01 p.m. is Okada, who left at 2:50 p.m. (he arrives before 3:00). Hashimoto (left at 3:00) would arrive at 3:05 and Someya (left at 3:10) at 3:15, both too late.

Diagram of the solution

Key Points

In an upside-down photo, both the order and the shapes of digits change
On a 7-segment display, 0, 1, 5 and 8 look the same when rotated
Once the time is fixed, check the travel time

Why people get fooled

You forget the premise that "it looked upside down" and read the digits in the photo as they are.

Similar tricks

The type that reads a rotated orientation
The type that layers on travel time

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