How many seconds will it take for a car that is traveling at a constant rate of 45 miles per
hour to travel a distance of 22 yards? (1 mile = 1,160 yards)
A. 8
B. 9
C. 10
D. 11
E. 12
GMAT Forum
5 postsPage 1 of 1
- RonPurewal
- Students
- Posts: 19744
- Joined: Tue Aug 14, 2007 8:23 am
http://s3.supload.com/free/conversion_p ... .jpg/view/
the link shows the work for using CONVERSION FACTORS to accomplish this conversion.
here are the basics of the process:
* start with the starting information, usually a concrete value. here, that concrete value is 22 yards.
note that rates are not "starting information"; those count as conversion factors.
* to accomplish the conversion, create CONVERSION FACTORS, which have EQUAL quantities on the top and bottom of the factor. there are two types of such conversion factors:
- RATES (which are naturally fractions already)
- REFERENCE CONVERSIONS (such as 12 inches = 1 foot) which are universally true and could be looked up in a reference book if necessary.
* position the fractions so that UNWANTED UNITS CANCEL and the desired units are left in the desired places.
- note how the 45 mph is positioned so that it's 1 hour per 45 miles, not 45 miles per 1 hour. this is done so that the miles are cancelled out.
--
in the problem shown, 22/1760 cancels down to 1/80, and 3600/45 cancels down to 80/1. therefore, 80/80 = 1, so the whole fraction gives 1 second. are you sure you didn't copy some number with an incorrect decimal place or other similar error?
plus, think about this intuitively: if a car is traveling at 45 miles per hour, which is approaching highway speeds, then it's ridiculous to think that it would take 8 to 12 seconds to travel 22 yards. the average human can run 22 yards in about three seconds. check the problem!
the link shows the work for using CONVERSION FACTORS to accomplish this conversion.
here are the basics of the process:
* start with the starting information, usually a concrete value. here, that concrete value is 22 yards.
note that rates are not "starting information"; those count as conversion factors.
* to accomplish the conversion, create CONVERSION FACTORS, which have EQUAL quantities on the top and bottom of the factor. there are two types of such conversion factors:
- RATES (which are naturally fractions already)
- REFERENCE CONVERSIONS (such as 12 inches = 1 foot) which are universally true and could be looked up in a reference book if necessary.
* position the fractions so that UNWANTED UNITS CANCEL and the desired units are left in the desired places.
- note how the 45 mph is positioned so that it's 1 hour per 45 miles, not 45 miles per 1 hour. this is done so that the miles are cancelled out.
--
in the problem shown, 22/1760 cancels down to 1/80, and 3600/45 cancels down to 80/1. therefore, 80/80 = 1, so the whole fraction gives 1 second. are you sure you didn't copy some number with an incorrect decimal place or other similar error?
plus, think about this intuitively: if a car is traveling at 45 miles per hour, which is approaching highway speeds, then it's ridiculous to think that it would take 8 to 12 seconds to travel 22 yards. the average human can run 22 yards in about three seconds. check the problem!
- PFWinkler
- Course Students
- Posts: 32
- Joined: Wed Aug 29, 2012 3:11 am
Re: Math - What's the quick way to solve this
Yes - There is a mistake here. It should be 220 yards....
Source is GMAT Prep
Source is GMAT Prep
- RonPurewal
- Students
- Posts: 19744
- Joined: Tue Aug 14, 2007 8:23 am
5 posts Page 1 of 1