Homework Help: math

Posted by bill on Sunday, January 21, 2007 at 12:53pm.

Ken's average driving speed is 25km/hr faster than Jim's. In the same length of time it takes Ken to drive 279 km, Jim drives only 204 km. What is Ken's average speed?

Possible Answers:

a) 93 km/hr
b) 118 km/hr
c) 43 km/hr
d) 68 km/hr

Let x equal the speed of Jim's car.

279/x + 25 = 204/x
204x + 5100 = 279x
5100 = 75x
5100/75 = 75/75x
x = 68km/h

Therefore the avg. speed of Jim's car is 68km/h. Since Ken's car is 25km/h faster...68+25 = 93km/h.
Therefore the avg. speed of Ken's car is 93 km/h.

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