GRE Prep Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Bob just filled his car's gas tank with 20 gallons of gasoho
[#permalink]
19 Feb 2019, 07:00
19 Feb 2019, 07:00
2
10
Bookmarks
00:00
Question Stats:
69% (02:08) correct
30% (02:32) wrong based on 111 sessions
Hide Show timer Statistics
Bob just filled his car's gas tank with 20 gallons of gasohol, a mixture consisting of 5% ethanol and 95% gasoline. If his car runs best on a mixture consisting of 10% ethanol and 90% gasoline, how many gallons of ethanol must he add into the gas tank for his car to achieve optimum performance?
A. 9/10
B. 1
C. 10/9
D. 20/19
E. 2
A. 9/10
B. 1
C. 10/9
D. 20/19
E. 2
Re: Bob just filled his car's gas tank with 20 gallons of gasoho
[#permalink]
19 Feb 2019, 11:26
19 Feb 2019, 11:26
1
let x be the amount of ethanol added.
1+x/19=1/9
By solving this equation we get x = 10/9
ans:c
1+x/19=1/9
By solving this equation we get x = 10/9
ans:c
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Re: Bob just filled his car's gas tank with 20 gallons of gasoho
[#permalink]
20 Feb 2019, 10:28
20 Feb 2019, 10:28
4
GreenlightTestPrep wrote:
Bob just filled his car's gas tank with 20 gallons of gasohol, a mixture consisting of 5% ethanol and 95% gasoline. If his car runs best on a mixture consisting of 10% ethanol and 90% gasoline, how many gallons of ethanol must he add into the gas tank for his car to achieve optimum performance?
A. 9/10
B. 1
C. 10/9
D. 20/19
E. 2
A. 9/10
B. 1
C. 10/9
D. 20/19
E. 2
Bob just filled his car's tank with 20 gallons of gasohol, a mixture containing of 5% ethanol and 95% gasoline.
5% of 20 gallons is 1 gallon.
So, PRESENTLY, there is 1 gallon of ethanol in the car's tank.
We want to add some PURE ethanol to the tank in order to get a 10% mixture of ethanol.
Let x = number of gallons of pure ethanol we ADD to the tank.
FACT #1: Once we add x more gallons of pure ethanol, the car's tank contains 1+x gallons of ethanol.
FACT #2: Once we add x gallons of ethanol, the car's tank contains a TOTAL of 20+x gallons of mixture.
We want the tank to have a 10% mixture of ethanol. In other words, we want the mixture in the tank to contain 1/10 ethanol.
So, we can write the equation: (1+x)/(20+x) = 1/10
Cross multiply to get: 10(1 + x) = 1(20 + x)
Expand: 10 + 10x = 20 + x
Rearrange: 9x = 10
Divide both sides by 9 to get: x = 10/9
Answer: C
Cheers,
Brent
