Carcass wrote:
A grocery store sells apples by the pound. If the price per pound is increased by $1, $12 will buy 0.4 pounds less of apples than if the price remains at the current level. What is the current price per pound of apples at the grocery store?
A. $4
B. $4.5
C. $5
D. $5.5
E. $6
Kudos for the right answer and explanation
Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITIONGRE - Math BookOne approach here is to test the answer choices.
There is an algebraic approach:
let
C = CURRENT price per poundSo,
C + 1 = INCREASED price per poundIf the price per pound is increased by $1, $12 will buy 0.4 pounds less of apples than if the price remains at the current level.Let's first turn this statement into a
word equationWe can write:
pounds of apples that can be purchased with $12 at CURRENT price - 0.4 =
pounds of apples that can be purchased with $12 at INCREASED price Convert to algebraic expression:
12/C - 0.4 =
12/(C + 1) Rewrite as: 12/C - 0.4C/C = 12/(C + 1)
Combine terms: (12 - 0.4C)/C = 12/(C + 1)
Cross multiply: (12 - 0.4C)(C + 1) = (12)(C)
Expand and simplify: -0.4C² + 11.6C + 12 = 12C
Rearrange: 0.4C² + 0.4C - 12 = 0
Multiply both sides by 10 to get: 4C² + 4C - 120 = 0
Divide both sides by 4 to get: C² + C - 30 = 0
Factor: (C - 5)(C + 6) = 0
So, EITHER C = 5 OR C = -6
Since C cannot have a NEGATIVE value, we can be certain that C = 5
Answer: C