Henry Ernest Dudeney/Puzzles and Curious Problems/48 - Robinson's Age

Puzzles and Curious Problems by Henry Ernest Dudeney: $48$

Robinson's Age

Robinson said.

My brother is two years older than I,

my sister is four years older than he,

my mother was $20$ when I was born,

and I was told yesterday that the average age of the four of is is $39$ years.

What was Robinson's age?

Sources

• 1932: Henry Ernest Dudeney: Puzzles and Curious Problems ... (previous) ... (next): Arithmetical and Algebraical Problems: Age and Kinship Puzzles: $48$. -- Robinson's Age
• 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Arithmetical and Algebraical Problems: Age Puzzles: $45$. Robinson's Age