Question 510514
Let {{{z}}} = Zoron's age now
Let {{{s}}} = his sister's age now
given:
{{{ z = s + 10 }}}
{{{ z + 3  = 2*( s + 3 ) }}}
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By substitution:
{{{ s + 10 + 3  = 2*( s + 3 ) }}}
{{{ s + 13 = 2s + 6 }}}
{{{ s = 13 - 6 }}}
{{{ s = 7 }}}
and
{{{ z = s + 10 }}}
{{{ z = 17 }}}
Zoron is 17 and his sister is 7
check:
In 3 years, he will be 20 and she will be 10
OK