<PRE><B>Question 1132768</B>
Let {{{ x }}} = ml of water at the start of 
Wednesday
At the end of Wednesday, there is
{{{ x - (1/2)*x + 200 = (1/2)*x + 200 }}} ml
in Sam&#39;s bowl
At the end of Thursdays, sam has:
{{{ (1/2)*x + 200 - (1/2)*( (1/2)*x + 200 ) }}}
{{{ (1/2)*x + 200 - (1/4)*x - 100 }}}
{{{ (1/4)*x + 100 }}}
You are told that:
{{{ (1/4)*x + 100 = 500 }}}
{{{ (1/4)*x = 400 }}}
{{{ x = 1600 }}}
There was 1600 ml at the start of Wednesday
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check:
Sam drinks half, so 800 ml is left
200 ml is added, so Sam has 1000 ml
at end of Wednesday
Sam drinks half, so 500 ml is left at end
of Thursday
OK
</PRE>