guerrero wrote:A reduction in the price of petrol by 10% enables a motorist to buy 5 gallons more for $180. Find the original price of petrol?
A. $11
B. $5
C. $45
D. $400
E. $4
OAE
We can plug in the answers, which represent the original price.
The correct answer choice is almost certainly a factor of $180 -- B, C, or E.
The price in answer choice C -- $45 per gallon -- seems way too high.
Answer choice B: 5
Number of gallons that can be purchased at the original price = 180/5 = 36.
Discounted price = 5 - .1(5) = 4.5.
Number of gallons that can be purchased at the discounted price = 180/4.5 = 40.
Increase in purchasing power = 40-36 = 4 gallons.
Doesn't work: the increase in purchasing power must be 5 gallons.
Eliminate B.
Answer choice E: 4
Number of gallons that can be purchased at the original price = 180/4 = 45.
Discounted price = 4 - .1(4) = 3.6.
Number of gallons than can be purchased at the discounted price = 180/3.6 = 1800/36 = 50.
Increase in purchasing power = 50-45 = 5 gallons.
Success!
The correct answer is
E.
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