Question 900429
The easiest way is to find a common denominator.  All of the denominators (10,5,4) go into 20.  Let's convert everything to 20ths.
{{{3/10}}}={{{6/20}}}
{{{2/5}}}={{{8/20}}}
{{{1/4}}}={{{5/20}}}
Now the equation becomes
{{{6/20}}}+{{{8/20}}}-{{{5/20}}}
{{{14/20}}}-{{{5/20}}}={{{9/20}}}