How can you compare prices at two different stores by finding the constant of proportionality

The constant of proportionality gives you the price per unit at each store.

Step-by-step explanation:

If you assume that the price (y) is directly proportional to the amount (x) you get, the formula is

y = kx

where k is the constant of proportionality.

k = y/x

k has the units of cost per unit, for example, dollars per ounce.

The fewer the dollars per ounce, the better the deal you are getting.

If store A offers apple sauce at $1.29 for 25 oz and Store B offers apple sauce at $2.89 for 50 oz, which is the better deal?

At store A, k = $1.29/25 oz = $0.052/oz or 5.2¢/oz

At store B, k = $2.89/50 oz = $0.058/oz or 5.8¢/oz

The apple sauce is cheaper at Store A.