Laura is stuck in aisle six at the supermarket trying to decide which jar of peanut butter to buy she can buy a 16-ounce jar for $2.59 or 24- ounce jar for $3.29. Which jar has a lower unit price per ounce? Show your calculations and reasoning. REAL ANSWERS ONLY

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  24-oz jar is lower cost per ounce

Step-by-step explanation:

The 16-ounce jar is almost $2.60. The 24-ounce jar contains half again as much peanut butter (16 +1/2·16 = 24). So, if the 24-ounce jar were the same price, it would cost half-again as much:

  $2.60 +(1/2)2.60 = $2.60 +1.30 = $3.90.

The 24-ounce jar is priced considerably below that amount, so the 24-ounce jar has a lower price per ounce.

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You could also view the 16-ounce jar as 2/3 the quantity of the 24-ounce jar. If it were the same price, that price would be about (2/3)$3.30 = $2.20. The 16-ounce jar is somewhat more than that, so costs more per ounce.

Additional comment

For the estimates we did here, we needed prices that were divisible by 2 or 3. That involved adding a penny to the given price. So, the estimated equivalent price is off by a penny or so--not an issue in this case.

Note that we didn't actually need to find the per-ounce prices. We only needed to find the price for an equivalent number of ounces, which is much easier mental arithmetic.

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step-by-step explanation: