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A car traveling at a certain constant speed takes 2 seconds [#permalink]
19 Jan 2008, 06:11

A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

A. 71.5 B. 72 C. 72.5 D. 73 E. 73.5

R 75 X T 1/75 hr D 1 1

2s/1*1min/60sec*1hr/60min

2/3600 --> 1/1800

1/75+1/1800 = Total time 5*5*3, 8*5*5*3*3 --> 24/1800 + 1/1800 --> 25/1800

A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

A. 71.5 B. 72 C. 72.5 D. 73 E. 73.5

When the car travels at 75 kmph, In 3600 sec --> 75 kms ? sec ---> 1 km

So for 1 km, 3600/75 = 48 sec.

From the problem, it takes 2 sec more than 48= 50 sec.

We want to know how long it takes to go 1,000 meters, so divide by 5 and multiply again by 4. 60/5=12*4=48 seconds.

Add 2 seconds to see 50 seconds to go 1,000 meters = divide by 5 and multiply by 6. 1,200 meters per minute. Multiply by 60 = 72,000 meters per hour.

72kmh

Answer B and you can do it all in your head

Your approach helpful, but I can still not get it. Why divide by 5, multiply by 4 and why divide by 5 and multiple by 6. I am a little confused. _________________