Question 154191
Let {{{f}}}= father's age now
Let {{{s}}}= son's age now
{{{f - 5}}}= father's age 5 years ago
{{{s - 5}}}= son's age 5 years ago
{{{f - 5 = 7*(s - 5)}}}
{{{f - 5 = 7s - 35}}}
{{{f = 7s - 30}}}
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{{{f + 5}}}= father's age in 5 years hence
{{{s + 5}}}= son's age in 5 years hence
{{{f + 5 = 3*(s + 5)}}}
{{{f + 5 = 3s + 15}}}
{{{f = 3s + 10}}}
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Set the 2 expressions for {{{f}}} equal to eachother
{{{7s - 30 = 3s + 10}}}
{{{4s = 40}}}
{{{s = 10}}}
Now substitute this in one of the equations
{{{f = 7s - 30}}}
{{{f = 7*10 - 30}}}
{{{f = 40}}}
The father is 40 and the son is 10