Professor Layton and the Diabolical Box
Puzzle 071: How Old Is She?
A 20-year-old says that when he was her age, she was half his current age, so how old is she?
- Chapter
- Chapter 5
- Location
- Cabaret · Ilyana
- Picarats
- 30 picarats
- Type
- Write Answer
- Region
- Same in all versions
Hint 1: A gentle nudge. Tap to flip.
Untangle the sentence one piece at a time.
Tap to flip backHint 2: The key idea. Unlocks after the previous card is flipped.
'Half my current age' is a fixed number. What is it?
Tap to flip backHint 3: Almost there. Unlocks after the previous card is flipped.
When the boy was her age, she was 10. How many years ago was that?
Tap to flip backAnswer: See the answer. Unlocks after the previous card is flipped.
The answer is 15.
Tap to flip backSolution, FAQ and sources
Solution
Let the girl be *g*.
1. Half the boy's current age is 10, so at some point in the past she was 10. 2. That moment was when the boy was *g*, which is 20 − *g* years ago. 3. Back then she was *g* − (20 − *g*) = 2*g* − 20. Set that equal to 10: 2*g* = 30, so *g* = 15.
Check: five years ago the boy was 15 (her age now) and she was 10 (half of 20). She's **15**.
About this puzzle
A boy tells a girl: “I’m 20 now. Back when I was as old as you are now, you were half my current age.” How old is the girl?
Unofficial fan guide, not affiliated with LEVEL-5 or Nintendo. Puzzle description, hints and solution written by Hint by Hint.
Similar puzzles: Puzzle 064: Stones in a Vase, Puzzle 060: Plaza Puzzle, Puzzle 059: A Ticket to Where?, Puzzle 072: Scrambled Photos
All Professor Layton and the Diabolical Box puzzles
FAQ
What is the answer to Puzzle 071, How Old Is She?, in Professor Layton and the Diabolical Box?
The answer is 15.
Where do you find Puzzle 071 in Diabolical Box?
Puzzle 071 appears in Chapter 5, in the Cabaret area, when you talk to Ilyana.
How many picarats is Diabolical Box Puzzle 071 worth?
30 picarats.
Sources
- Professor Layton Wiki (Fandom): Puzzle:How Old Is She?
- StrategyWiki: Professor Layton and the Diabolical Box/Puzzles 51-75
- Professor Layton Wiki (Fandom): Module:PuzzleData/DB
Facts checked on November 14, 2026
Unofficial fan guide. Not affiliated with, endorsed by, or sponsored by LEVEL-5 Inc. Professor Layton, The New World of Steam, and all related names, characters, and trademarks are the property of their respective owners.