Brand w: 500 napkins for $2.87
brand x: 200 napkins for $1.27
brand y: 100 napkins for $0.62
brand z: 250 napkins for $1.37

which brand is the cheapest? what is the cost of one napkin of this brand?

which brand is the most expensive? what is the cost of one napkin of this brand?

The best way, in my opinion, to do this, is to find the unit rate of each napkin brand, or the cost per napkin. To do this, divide the money amount by the amount of napkin they give you.

     /Brand W:2.87/500=.00574  \
     \Brand X: 1.27/200=.00635   \     These are the
     /Brand Y: .62/100  =.0062     /     cost per napkin.
    \Brand Z:  1.37/250=.00548  /

Which one out of these 4 values is the lowest value? Obviously the two with the 6 in the thousandths place are more expensive than the ones with the 5s in the thousandths place, so that already eliminates Brand Z and Brand W.

What do we have left?

Brand X: 1.27/200=.00635 
Brand Y: .62/100  =.0062  
     Cool. Which of these is a smaller number? Tip: If the first number besides 0 is the same, check the next one! You should get that Brand Y is the cheapest! :) Hoped this helped!