Question 940379
Let {{{ n }}} = number of years from now
when father is twice as old as son
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{{{ 42 + n = 2*( 12 + n ) }}}
{{{ 42 + n = 24 + 2n }}}
{{{ n = 42 - 24 }}}
{{{ n = 18 }}}
In 18 yrs, father is twice as old as son
check:
{{{ 42 + 18 = 60 }}}
{{{ 12 + 18 = 30 }}}
OK