What the boy says to the girl can be written as x = y - 1.

The answer that the sister gives her brother can be written as:

y = 2(x - 1) or y = 2x - 2Substituting x = y - 1 gives us y = 4 and hence x = 3.

There are therefore seven children in the family.

Source: Berrondom, Marie

Categories: Reasoning, Number sense, Algebra

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