Let the father’s age be F, which equals children’s sum S. In 20 years, children gain 4 × 20 = 80 years: F + 80 = 2(F + 20). This gives F + 80 = 2F + 40, so F ...
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Let the father’s age be F, which equals children’s sum S. In 20 years, children gain 4 × 20 = 80 years: F + 80 = 2(F + 20). This gives F + 80 = 2F + 40, so F ...