Question 1011568
Let younger sister's age  = {{{ x }}}
Her older sister's age is {{{ x + 4 }}}
The brother's age is {{{ x - 4 }}}
The younger sister plus brother's age = {{{ 16 }}}
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{{{ x + x - 4 = 16 }}}
{{{ 2x = 20 }}}
{{{ x = 10 }}}
and
{{{ x + 4 = 14 }}}
and
{{{ x - 4 = 6 }}}
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The younger sister is 10 
Her older sister is 14
The brother is 6