GMAT Prep - rates

caramel3536 · Posted: Fri May 09, 2008 3:13 pm Post subject: GMAT Prep - rates

On his trip from Alba to Benton, Julio drove the first x miles at an avg rate of 50 m/hr and the remaining distance at an avg rate of 60m/hr. How log did it take Julio to drive the first X miles?
(1) On this trip, Julio drove for a total of 10 hours and a total of 530 miles
(2) On this trip, Julio took 4 more hours to drive the first x miles than to drive the remaining distance

ans (d)

VP_Tatiana · Posted: Sat May 10, 2008 5:38 pm Post subject:

I think that the answer to this problem would be A.

First of all, we need to keep in mind our trusty formula d = rt (distance = rate * time).

We have a rate (which we can express as a function of x) in the question stem, and we get a distance and a time in (I). We have one equation and one unknown, so that's enough info to solve the question.

If you wanted to solve, which you don't need to do here, you would have the formula.

530 = r * 10

Rate is calculated as a weighted average:

r = (x/530)(50) + ((530 - x)/530)(60)

(see, you really don't want to do the math here if you don't have to...)

Anyway, one eq. one unknown - (I) is sufficient.

I approach (II) by thinking about the two distinct legs of the journey - the journey to mile x, and the journey after that.

To set up my d = rt, I have:

x = 50 * t1
total dist - x = 60 * (t1 - 4)

We add them together and get total dist = (50 * t1) + (60 * (t1 - 4)). We can't solve for t1 because we don't have total distance. So, (II) is not sufficient.

Since (I) is sufficient, and (II) is not sufficient, the answer is A.

moneyman · Posted: Sun May 11, 2008 4:11 am Post subject:

I agree..the answer should be A

Distance = Rate * Time

According to the question,

x=50*T1------>(a)

(d-x)=60*T2------->(b)

We need to find T1

(1) says x+(d-x)=530 or d=530 substitute this value in (a) to get T1

(2) says T1=T2+4 but we are not given any additional information..So its INSUFFICIENT

Hence ans A

amitansu · Posted: Mon May 12, 2008 2:01 am Post subject:

Ans A here.

For statement 2, i tried for a whole half hour but to end up with no answer !!