Question 870728
Let {{{ s }}} = his son's age now
{{{ 7s }}} = Remain's age now
{{{ s + 10 }}} = his son's age in 10 years
{{{ 7s + 10 }}} = Remain's age in 10 years
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{{{ 7s + 10 = 3*( s + 10 ) }}}
{{{ 7s + 10 = 3s + 30 }}}
{{{ 4s = 20 }}}
{{{ s = 5 }}}
and
{{{ 7s = 7*5 }}}
{{{ 7s = 35 }}}
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His son's age now is 5
Remain's age now is 35 
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check:
{{{ 7s + 10 = 3*( s + 10 ) }}}
{{{ 7*5 + 10 = 3*( 5 + 10 ) }}}
{{{ 35 + 10 = 3*15 }}}
{{{ 45 = 45 }}}
OK