Question

The total ager of father and son is 100 years. Thirty years ago the age of father was 3 times greater than the age of his son. What is the age of the son at present ? ​

Answer 1

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$\tt{let \: the \: age \: of \: father \: be \:, x} \\ \\ \tt{sum \: of \: father^,s \: age \: and \: son^,s \: age \:} \\ = \tt100 \\ \\ \tt{sons^,s \: age = 100 - x} \\ \\ \\\tt\underline {30 \: years \: ago} \\ \\ \tt{age \: of \: father \: = x - 30} \\\tt age \: of \: son = 100 - x - 30 = 70 - x \\ \\\tt (x - 30) = 3(70 - x) \\ \\\tt x - 30 = 210 - 3x \\ \tt4x = 240 \\ \\\tt x = 60 \\ \\\tt present \: age \: of \: son \\ = \tt100 - x = 100 - 60 \\ = \large\bf\color{lime}\tt\underline{\underline{40}}$