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Re: Each day after today, the price of gas, in cents per gallon, increases [#permalink]
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Bunuel wrote:
Each day after today, the price of gas, in cents per gallon, increases 5 cents per day. The day after the price reaches twice its current level, the price falls by 25% but then continues the pattern of increasing 5 cents per day. How much does a gallon of gas cost, in cents, at the end of 25 days, if the price today is 95 cents a gallon?

A. 165
B. 167.5
C. 170
D. 172.5
E. 175


Current Price = 95 cents

To double the price (i.e.2*95=190) the price need to increase by 95 cents @5 cents a day rate so total days = 95/5 = 19 days

so after 19 days the price falls to 190-(25/100)*190 = 142.5

so next 6 days (25-19=6 days) the increase = 6*5 = 30 cents

So total price of gasoline after 25 days = 142.5+30 = 172.5 cents

Answer: Option D
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Re: Each day after today, the price of gas, in cents per gallon, increases [#permalink]
Expert Reply
Bunuel wrote:
Each day after today, the price of gas, in cents per gallon, increases 5 cents per day. The day after the price reaches twice its current level, the price falls by 25% but then continues the pattern of increasing 5 cents per day. How much does a gallon of gas cost, in cents, at the end of 25 days, if the price today is 95 cents a gallon?

A. 165
B. 167.5
C. 170
D. 172.5
E. 175


I think this one comes down to tracking on days very carefully. It's day 21 that reboots the "plus 5 cents a day" cycle. And there are FIVE days, inclusive, between days 21 and 25.

Today = Day 0 = 95 cents

Tomorrow =
Day 1 = +5 = 100 cents
Day 2 = +5 = 105 cents
.
.
Day 19 = +5 = 190 cents

(Or, we need 95 to double, i.e., we need TWO 95s. How many days to get another 95? 95/5 = 19.)

Day 20=75% of 190 = 142.5 cents
Day 21 = +5 cents
Day 22 = +5 cents
Day 23 = +5 cents
Day 24 = +5 cents
Day 25 = +5 cents

Total added Days 21-25: 25 cents

142.5 + 25 = 167.5 cents

Thought it would take forever. Shocked myself :shock: :) to discover that this brute force instance took 2:26.

Answer B.
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Re: Each day after today, the price of gas, in cents per gallon, increases [#permalink]
mohshu wrote:
double as in the cost becomes 190 cents,..in 19 days,,,
but falls by 25% = 142.5 cents

remaining 6 days it rises by 6 * 5 = 30

142.5 + 30 = 172.5

ans D



Hi,
can you let me know where i am wrong,
i got B as the answer , see its written in stem that the day after the prices reaches its current levels means after 19 days so on 20th day the price would be 142.5 so for the next 5 days the pattern continues then in 25 days the price will be 167.5 cents .

please let me know whether i am wrong or missed something .

thanks
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Re: Each day after today, the price of gas, in cents per gallon, increases [#permalink]
Bunuel wrote:
Each day after today, the price of gas, in cents per gallon, increases 5 cents per day. The day after the price reaches twice its current level, the price falls by 25% but then continues the pattern of increasing 5 cents per day. How much does a gallon of gas cost, in cents, at the end of 25 days, if the price today is 95 cents a gallon?

A. 165
B. 167.5
C. 170
D. 172.5
E. 175



Bunuel is the answer of the above question option D?



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