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A question from GMAT Prep I get wrong all the ways I did. Anybody knows how to do this

Did it take Pei more than 2 hours to walk a distance of 10 miles along a certain trail ( i mile =1.6km rounded to nearest tenth)

1 Pei walked the distance at an average rate of less than 6.4 km/hr.

2 On average it took Pei more than 9 minutes per km to walk the distance .

Is the answer D?

1. At most, Pei walked 12.8km in 2 hours. Since the trail is 16km long, then we know that Pei took more than 2 hours. Therefore, statement 1 is sufficient

2. At the fastest, Pei walked 1 km in 9 minutes. Then to walk 16km, the Pei needs 144 minutes, which is more than 2 hours. Therefore, statement 2 is sufficient.

A question from GMAT Prep I get wrong all the ways I did. Anybody knows how to do this

Did it take Pei more than 2 hours to walk a distance of 10 miles along a certain trail ( i mile =1.6km rounded to nearest tenth)

1 Pei walked the distance at an average rate of less than 6.4 km/hr.

2 On average it took Pei more than 9 minutes per km to walk the distance .

I say D.

first, conversions: 10 miles = 16 km

2 hours = 120 minutes

1) less than 6.4km/hr - you want to know if it took less than 2 hours. 6.4 x 2 = 12.8km in two hours, when she has to go 16. You can answer the question if it took more than 2 hours.

Sufficient, eliminate B, C, & E.

2) 9 minutes per km - you want to know if it took less than 2 hours. 16km x 9min = 144 minutes for 16 km, when 120 minutes = 2 hours. You can answer the question if it took longer than two hours.

here is my calculation: if it takes 1 hour to walk max 6.4 km if will take max. 2.5 hours to walk 16 km.

since it says average rate less than 6.4 so time is less than 2.5 but it could be less than 2. so im getting that A is not suff. whats wrong with my method ? pls explain

here is my calculation: if it takes 1 hour to walk max 6.4 km if will take max. 2.5 hours to walk 16 km.

since it says average rate less than 6.4 so time is less than 2.5 but it could be less than 2. so im getting that A is not suff. whats wrong with my method ? pls explain

distance=rate*time --> rate and time are inversely proportional, which means that if you increase the rate then you'll need less time to cover the same distance and if you decrease the rate you'll need more time to cover the same distance.

So, rate is less than 6.4 kilometers per hour means that time needed to cover 16 kilometers is more than 2.5 hours.

Alternate approach:

Did it take Pei more than 2 hours to walk a distance of 10 miles along a certain trail? (1mile = 1.6 Kilometers, rounded to the nearest tenth)

Basically the question asks whether the rate was less than 10/2=5 miles per hour: is rate<5 miles per hour? Because if it is less than 5 miles per hour, then time needed to cover 10 miles would be more than 2 hours.

(1) Pei walked this distance at an average rate of less than 6.4 kilometers per hour --> rate<6.4 kilometers per hour --> 6.4 kilometer = 6.4/1.6 = 4 miles --> rate<4 miles per hour. Sufficient.

(2) On average, it took Pei more than 9 minutes per Kilometers to walk this distance --> more than 9/60 hours to cover 1 kilometer --> rate<60/9 kilometers per hour (time more - rate less) --> 60/9 kilometers = (60/9)/1.6 = ~4.2 miles --> rate<4.2 miles per hour. Sufficient.

here is my calculation: if it takes 1 hour to walk max 6.4 km if will take max. 2.5 hours to walk 16 km.

since it says average rate less than 6.4 so time is less than 2.5 but it could be less than 2. so im getting that A is not suff. whats wrong with my method ? pls explain

distance=rate*time --> rate and time are inversely proportional, which means that if you increase the rate then you'll need less time to cover the same distance and if you decrease the rate you'll need more time to cover the same distance.

So, rate is less than 6.4 kilometers per hour means that time needed to cover 16 kilometers is more than 2.5 hours.

Alternate approach:

Did it take Pei more than 2 hours to walk a distance of 10 miles along a certain trail? (1mile = 1.6 Kilometers, rounded to the nearest tenth)

Basically the question asks whether the rate was less than 10/2=5 miles per hour: is rate<5 miles per hour? Because if it is less than 5 miles per hour, then time needed to cover 10 miles would be more than 2 hours.

(1) Pei walked this distance at an average rate of less than 6.4 kilometers per hour --> rate<6.4 kilometers per hour --> 6.4 kilometer = 6.4/1.6 = 4 miles --> rate<4 miles per hour. Sufficient.

(2) On average, it took Pei more than 9 minutes per Kilometers to walk this distance --> more than 9/60 hours to cover 1 kilometer --> rate<60/9 kilometers per hour (time more - rate less) --> 60/9 kilometers = (60/9)/1.6 = ~4.2 miles --> rate<4.2 miles per hour. Sufficient.

Speed = S mph Distance = 10 miles Ques = Was the time greater than 2 hours?

If S X 2 = 10, speed becomes 5 mph

when Distance is constant, speed decreases as the time increase. So for Time to be greater than 2 hours, speed should be less than 5 mph

So the question can be rephrased as "Was the speed less than 5mph?"

S1) Speed was less than 6.4 KMPH -----> Speed was less than 4 mph -----Sufficient

S2) Pie took more than 9 minutes per km to walk ------------> S X \(\frac{9}{60}\) = 1 -----> S = 6.66 -------> Speed was less than 6.66 kmph -----------> Speed was less than 4.xxx mph --- Sufficient

Re: Did it take Pei more than 2 hours to walk a distance of 10 [#permalink]

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28 Jul 2013, 10:42

1

This post received KUDOS

Did it take Pei more than 2 hours to walk a distance of 10 miles along a certain trail ( i mile =1.6km rounded to nearest tenth)

Because both statements are in km, let's convert miles to km:

Did it take Pei more than 2 hours to walk a distance of 16km?

(1) Pei walked the distance at an average rate of less than 6.4 km/hr.

With #1, the fastest Pei could have walked in two hours was 12.8km which is far short of the 16km the question asks. Therefore, Pei took more than 2 hours to walk 16km. SUFFICIENT

(2) On average it took Pei more than 9 minutes per km to walk the distance. The stem tells us that Pei walked 16km. If his average was at a minimum, 9minutes/km then it would have taken him minimally 9minutes/16km = 151 minutes which is obviously greater than 120 minutes/2 hours. SUFFICIENT

Re: Did it take Pei more than 2 hours to walk a distance of 10 [#permalink]

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24 Jul 2015, 01:41

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