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average speed

by gmat009 » Sat Nov 15, 2008 10:29 pm
The time it took car A to travel 400 miles was 2 hours less than the time it took car B to travel the same distance. If car A's average speed was 10 miles per hour greater than that of Car B, what was car B's average speed, in miles per hour?

a)20
b)30
c)40
d)50
e)80
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Re: average speed

by iamcste » Sat Nov 15, 2008 10:38 pm
gmat009 wrote:The time it took car A to travel 400 miles was 2 hours less than the time it took car B to travel the same distance. If car A's average speed was 10 miles per hour greater than that of Car B, what was car B's average speed, in miles per hour?

a)20
b)30
c)40
d)50
e)80
Tb-TA=2

(400/x)-(400/x+10)=2


solve it to get ( Xsquare)+10x-200=0

X=40, X=-50

Speed cannot be negative, hence X=ans=B speed=40 miles/hr
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Re: average speed

by logitech » Sat Nov 15, 2008 10:42 pm
gmat009 wrote:The time it took car A to travel 400 miles was 2 hours less than the time it took car B to travel the same distance. If car A's average speed was 10 miles per hour greater than that of Car B, what was car B's average speed, in miles per hour?

a)20
b)30
c)40
d)50
e)80
You can either solve this with Distance = Velocity x Time or use the options, which will save you time with these type of questions:

Also remember the answer choices are designed so you can make a mistake and choose A's average speed instead of B

A is faster than B ( 10 mph)

Look at the answer choices:

20-30
40-50
80 - MOST LIKELY A WRONG CHOICE with no match

So lets start with 20-30, Distance is 400 so 400/30 will be an ugly number ;-) which sends me automatically to 40-50 pair

400/40 = 10
400/50 = 8

50-40=10 :idea:

B=40 :!:
LGTCH
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