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Stupid Carlos!

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Stupid Carlos!

by KICKGMATASS123 » Tue May 19, 2009 6:03 pm
If it took Carlos 1/2 hour to cycle from his house to the library yesterday, was the distance that he cycled greater than 6 miles? (Note: 1 mile=5280 feet.

1) The average speed at which Carlos cycled from his house to the library yesterday was greater than 16 feet per second.

2) The average speed at which Carlos cycled from his house to the library yesterday was less than 18 feet per second.

OA is E

I dont understand why its not B.

Avg speed = total distance/ total time??

1. I worked with the avg speed of 17feet per second
2. I worked with the avg speed of 15 feet/ sec

Pls help.. I dont know what I'm doing wrong..
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by tdadic84 » Tue May 19, 2009 6:26 pm
ok..first calculate 6 miles = 31,680 feet
then seconds in 1/2 and hour = 1800 seconds

1. so it says his speed was GREATER then 16 feet/sec...

so...16 X 1800 = 28,800 FEET...therefore it was greater then 28,800..so it can be 30,000 feet or 40,000 feet...therefore

insuff...


2. says he cycled at 18 feet per second...

so 18 X 1,800 = 32,400 feet...therefore..we coould have cycled 33,000 or 32,000

insuff...

Take them together...we still dont kno if he cycled a distance greater then 31,680 feet.

hence E
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by lunarpower » Wed May 20, 2009 3:46 am
solid approach, but you fumbled on some of the specific numbers:
tdadic84 wrote:so 18 X 1,800 = 32,400 feet...therefore..we coould have cycled 33,000 or 32,000
this should say "32,000 or 31,000", where the point is that the former is above the threshold value of 31,680 and the latter is below that threshold value.

33,000 is actually an impossible value, since we know that carlos cycled less than 32,400 feet.

other than that (which may just be a typographical error), right on.
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by m&m » Wed May 20, 2009 10:58 am
Fully agree with above but I did it in terms of ft/sec which is a nicer/smaller number to deal with.

So (5280 ft/mi * 6 mi) / (30 mins * 60 sec/min) --> 17.6 using some quick crossing out you get 528/30 and you can divide to get 17 R 18. SO around 17.6 (turns out it's exactly that)

so rewording we get did Carlos travel at AT LEAST 17.6 ft/sec

in A we have >17 --> if we assume it 17.1 then he's going too slow but it could be 18, which would be too fast --> insuff

in B we have <18 --> so at 17.9 he's too fast but at 17 he's too slow --> insuff

A&B he could be going at 17.1 too slow or max 17.9 too fast -->insuff

so E
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