A health food company packs almond butter in jars. Some jars hold 250 g. Other jars hold 500 g. On Tuesday, the company packed 186.5 kg of almond butter in 511 jars. How many jars of each size did they pack?

Let the number of 250g=0.25  kg jars be x and that of 500g=0.5 kg jams be y;
therefore:
total number of jars ws
x+y=511
x=511-y..........i

total mount kgs was:
0.25x+0.5y=186.5....ii
substituting i in ii
0.25(511-y)+0.5y=186.5
127.75-0.25y+0.5y=186.5
solving for y we get:
0.25y=186.5-127.75
0.25y=58.75
y=58.75/0.25
y=235 jars
and 
x=511-x
=511-235
=276
hence we conclude that there was 235 jars with 0.5 kg almond and 276 jars with 0.25 kg almonds