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Re: Time, Speed, Distance Problem [#permalink]
09 Sep 2009, 17:40

1

This post received KUDOS

virtualanimosity wrote:

Q. In a race of 600m,Bryan beats Roger by 60m and in a race of 500 m Roger beats Andy by 25m. By how many metres will Bryan beat Andyin a 400 m race?

1. 48m 2. 52m 3. 56m 4. 58m

Yeah this may look like RTD problem, but its not. Its a simple ratio problem

Race between Bryan and Roger - Roger covers 10% less of the distance i.e. in 600 m race, Roger covers 60 m less than Bryan. So in a 400 m race, Roger would cover 40 m less than Bryan i.e. 360 m

Race between Roger and Andy - Andy covers 5% less distance than Roger (In 500m race, Andy covers 25 m less than Roger). So when Roger covers 360 m, Andy would cover 5 % less - i.e. 342 m.

Distance difference between Bryan and Andy in a 400 m race = 400 - 342 = 58

Re: Time, Speed, Distance Problem [#permalink]
10 Sep 2009, 00:25

1

This post received KUDOS

When bryan runs 600 metres, roger can run 540 metres. i.e. when bryan runs 400 metres, roger can run 360 metres. When roger run 500 metres, andy can run 475 metres. i.e. when roger runs 360 metres, and can run 342 metres. So when bryan runs 400 metres, roger can run 360 and andy can run 342 metres

Re: Time, Speed, Distance Problem [#permalink]
10 Sep 2009, 06:07

Race 1: Bryan and Roger Roger has covered 10% less of the distance 600m Roger ll cover 60 m less than Bryan. So in a 400 m race, Roger would cover 10% of 400 = 40 m less than Bryan i.e. 360 m

Race 2:Roger and Andy Andy has covered 5% less distance than Roger. So in 360 m, Andy would cover 5 % less - i.e. 342 m.

Re: Time, Speed, Distance Problem [#permalink]
11 Sep 2009, 12:28

600=60 (min) * 10km/h Bryan 540=60 (min) * 9km/h Roger

500= 9km/h *55.5 (min) Roger 475= 8.55 km/h *55.5 (min) Andy

400=10km/h*40 min Bryan 342 = 8.55 km/h *40min Andy

400-342=58 _________________

Trying to make CR and RC my strong points

"If you want my advice, Peter," he said at last, "you've made a mistake already. By asking me. By asking anyone. Never ask people. Not about your work. Don't you know what you want? How can you stand it, not to know?" Ayn Rand

Re: Time, Speed, Distance Problem [#permalink]
05 Nov 2011, 04:55

virtualanimosity wrote:

Q. In a race of 600m,Bryan beats Roger by 60m and in a race of 500 m Roger beats Andy by 25m. By how many metres will Bryan beat Andyin a 400 m race?

1. 48m 2. 52m 3. 56m 4. 58m

Since on the first race (600m), Bryan and Roger run for the same time

their ratio of distance run, will be the same with the ratio of their speeds:

Speed Bryan : Speed Roger ---> 600:540 ---> 10:9

Since on the second race (500m), Roger and Andy run for the same time:

their ratio of distance run, will be the same with the ratio of their speeds:

Speed Roger : Speed Andy ---> 500:475 ---> 20:19

The ratio of their speed's will be:

Speed of Bryan : Speed of Roger : Speed of Andy ---> 200 : 180 : 171

On the third race (400m), we assume that Bryan and Andy Run for the same time and will try to find their distance when Bryan finishes (when he covered 400m). Because they run for the same time, their ratio of speeds will equal the ratio of distance run.