Answer:
5-pound bag
Explanation:
You want to know which of 5 pounds for $1.68 or 6 pounds for $2.47 is a better buy.
Relative cost
You can go to the trouble to find the per-pound cost of each bag. Or, you can compare relative cost to relative weight.
The 6-pound bag, at about $2.40 is 50% more than the 5-pound bag, at about $1.60. The weight of the 6-pound bag is 20% more than the weight of the 5-pound bag. (6/5 = 1.20 = 120%)
When you spend $2.47 for a 6-pound bag, you're paying 50% more for 20% more soil, not a good deal.
The better buy is the 5 pound bag.
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Additional comment
The actual price difference is 2.47/1.68 -1 ≈ 0.47, or 47%, reasonably close to our 50% estimate.
Another way to consider the question is to realize that 6 pounds is 20% more than 5 pounds, and 20% more than the 5-pound price is 1.68 +2(.168) ≈ 2.02. At the 5-lb price you could get 6 lb for $2.02, not $2.47.
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