Question 982871
They don't mention any units, so I can make
up a unit called U such that the 1st vat 
contains {{{ 100 }}} U of OJ
--------------------------------
I pour {{{ .1*100 = 10 }}} U into the 2nd vat
The 1st vat now has {{{ 100 - 10 = 90 }}} U
of OJ
------------
Let {{{ x }}} U = Amount of OJ now in 2nd vat
{{{ 90 = 3x }}}
{{{ x = 30 }}}
--------------
Before I added the {{{ 10 }}} U, the 2nd vat had 
{{{ 30 - 10 = 20 }}} U of OJ
-------------------------
The % increase in the 2nd vat was:
{{{ (10/20)*100 = 50 }}}%