Question 800897
Let {{{ a }}} = Ana's age now
Let {{{ m }}} = Maria's age now
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The difference in their ages never changes,
so it remains equal to {{{ m - a = 36 - a }}}
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I'll start at the end:
" when Maria was as old as Ana is now "
This says when Maria's age was equal to {{{ a }}}
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When Maria was {{{ a }}}, Ana was {{{ a }}} minus
the difference in their ages, or
{{{ a - ( m - a ) = a - ( 36 - a ) }}}
{{{ a - 36 + a = 2a - 36 }}}
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Maria is twice this age, so
{{{ 36 = 2*( 2a - 36 ) }}}
{{{ 36 = 4a - 72 }}}
{{{ 4a = 108 }}}
{{{ a = 27 }}}
Ana is 27 now
check:
" when Maria was as old as Ana is now "
when Maria was {{{ 27 }}}
Ana was {{{ 27 - ( 36 - 27 ) }}}
{{{ 27 - 36 + 27 = 54 - 36 }}}
{{{ 54 - 36 = 18 }}}
Maria is twice this age
{{{ 36 = 2*18 }}}
OK