This classic logic puzzle often goes like this:
“When I was [age], my sister was half my age. Now I’m 54. How old is she now?”
At first glance, it seems like we’re missing information — and we are. But the trick is understanding that the age difference between siblings never changes.
Step 1: Understand the key idea
If at some point:
Your age = x
Your sister’s age = x/2
Then the difference is:
x − x/2 = x/2
So your sister is always younger by x/2 years.
Step 2: The missing assumption (the key to solving itIn this well-known puzzle, the hidden standard case is:
When you were 10 years old, your sister was 5 years old
