The Four-Lamp Code

Difficulty ★☆☆about 4 minEveryday MysteryBinary numbersCodes

Four lamps worth 8, 4, 2, 1 from left to right. Lit means the value counts. On, off, on, on?

Case Record

Beside the vault door are four lamps in a row. The code is the number the lamps show. A note says:

"The lamps, from the left, are worth 8, 4, 2 and 1. A lit lamp counts, an unlit one does not. Add up the lit values to get the code."

Right now, from the left, the lamps are lit, unlit, lit, lit.

Your question

What is the code?

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

Open hint 1

Which lamps are lit?

Open hint 2

What is each lamp worth?

Open hint 3

Add them up.

Your question

What is the code?

Choose the answer closest to the truth.

The answer is: 11.

The lit lamps are the first (8), the third (2) and the fourth (1). 8 + 2 + 1 = 11. In binary this is written 1011, which is 11 in decimal.

Diagram of the solution

People forget the place values or add the unlit lamps.

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