Certain approaches lead to an early total of nineteen people. The addition of nine sons, nine sisters, and one father produces that number. The structure of the sentence contains the source of the common error.

The riddle states that a man has nine sons. It states that each son has a sister. The wording does not specify separate sisters for each son.

All nine sons may share one sister. That possibility holds the key.

A careful breakdown follows.

Nine sons form the first group.

One sister forms the sibling shared among the sons.

One father forms the parent of the children.

The total becomes nine plus one plus one. The sum equals eleven people.

The solution emerges through close attention to the given words.

Many individuals reach an incorrect total because of the way the sentence is constructed. The phrase “each son has a sister” leads the mind toward an image of multiple distinct sisters. The assumption of uniqueness appears automatically.

This riddle illustrates the value of careful attention to language. The exercise functions as a measure of reading comprehension. It measures logical sequencing. It measures the capacity to hold back from automatic assumptions.

The experience points toward a broader observation that applies in daily situations. Appearances at first glance may require further examination.

A step-by-step path leads to the correct total.

Begin by counting the sons. The number stands at nine.

Continue by counting the sister. The number stands at one, shared by the group of sons.

Add the father. The number stands at one.