Question 1053910
You have two significant figures in each piece of numeric information.  


x and y, pounds of cheap and expensive ingredient feed items;


{{{system(x+y=34,0.28x+0.52y=0.42*34)}}}


{{{28x+52y=42*34}}}
{{{7x+13y=21*17}}}


{{{y=34-x}}}
substitute into the money or price equation now which has been simplified.
{{{7x+13(34-x)=21*17}}}
{{{7x+442-13x=357}}}
{{{-6x=357-442}}}
{{{6x=85}}}
{{{x=86/6}}}
{{{highlight(x=14&1/6)}}}, or decimalized, {{{highlight(x=14.166666repeating=14.17)}}}


Look very closely at the given 34 pounds of mixture feed to make.  This IS to the nearest whole pound, the nearest 1 pound.  Just how finely can the feed ingredients be measured?  Are you allowed to the nearest half pound, or nearest quarter pound, or maybe the nearest one-ounce?  No indication.  You are only given,  "make a 34 pound bag of feed".  You are not given any assumptions to use; no mention of any accuracy needed other than your two significant figures for all given information.  If this is the only way your facts are given, then your answer for the cheap feed, x, should be 14, because the computed {{{14&1/6=14.17}}} will only be read or measured at best without any assumptions, to 14, because 14.17 is closer to 14 than to 15.