Which is the better deal? 5 pounds of apples for $4.25 or 8 pounds of apples for $6.56 why?

What you do is divide $4.25 by 5 and divide 6.56 by 8. The price per apple for the 5 lb. is $0.85, and for the 8 lb. is $0.82. Since $0.82 is less, that is the best deal.

8lbs for $6.56

Work for 5lbs for $4.25: 
$4.25 divided by 5 to get the price per pound. ($0.85/lb)

Work for 8lbs for $6.56:
$6.56 divided by 8 to get the price per pound. ($0.82/lb)