capacity and rate problem :) !!!!!!!! thankssssssss

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charmaine: Senior | Next Rank: 100 Posts; Posts: 71; Joined: Sun May 18, 2008 11:04 pm; Thanked: 1 times

capacity and rate problem :) !!!!!!!! thankssssssss

by charmaine » Wed Sep 10, 2008 11:08 pm

11. If 6 gallons of gasoline are added to a tank that is already filled to 3/4 of its capacity, the tank is then filled to 9/10 of its capacity. How many gallons does the tank hold?
(A) 20
(B) 24
(C) 36
(D) 40
(E) 60

ans. c

12. A bus trip of 450 miles would have taken 1 hour less if the average speed S for the trip had been greater by 5 miles per hour. What was the average speed S, in miles per hour, for the trip?
(A) 10
(B) 40
(C) 45
(D) 50
(E) 55

ans.E

Quote

Source: Beat The GMAT — Problem Solving | Wed Sep 10, 2008 11:08 pm

parallel_chase: Legendary Member; Posts: 1153; Joined: Wed Jun 20, 2007 6:21 am; Thanked: 146 times; Followed by:2 members

Re: capacity and rate problem :) !!!!!!!! thankssssssss

by parallel_chase » Thu Sep 11, 2008 12:58 am

charmaine wrote:11. If 6 gallons of gasoline are added to a tank that is already filled to 3/4 of its capacity, the tank is then filled to 9/10 of its capacity. How many gallons does the tank hold?
(A) 20
(B) 24
(C) 36
(D) 40
(E) 60

ans. c

let x be the total capacity
3x/4 + 6 = 9x/10
x = 40

if the question is asking about total capacity 40 is the answer.

if the question is asking about 9/10 of its capacity answer is 36.

Since it is not clear from the question, i presume that this is not the real GMAT question.

12. A bus trip of 450 miles would have taken 1 hour less if the average speed S for the trip had been greater by 5 miles per hour. What was the average speed S, in miles per hour, for the trip?
(A) 10
(B) 40
(C) 45
(D) 50
(E) 55

ans.E

OA should be 45.

450 = s*t

450 / s = t

450 = (s+5)*(t-1)

substitute the value for t

450/(s+5) = (450/s - 1)

solve for s, you will get two values s=45, s=-50

s cannot be -50 since the speed cannot be negative, therefore 45 is the answer.

I think the OA for this answer is wrong. Whats the source??