You drive 200 miles to city at an average speed 10 miles per hour faster than your usual average speed. If you completed the trip in 1 hour less than usual. What is your usual driving speed, in miles per hour?

Question

anonymous · Answer

d=(r)(t)

anonymous · Answer

please help!!!

anonymous · Answer

d=rt    200=(s+10)(t-1)

anonymous · Answer

d=rt  200=rt

anonymous · Answer

200= rt-r+10t-10      200=200-r+10t-10        200=190-r+10t

anonymous · Answer

200-190=-r+10t      10=-r+10t

anonymous · Answer

r=10t-10

anonymous · Answer

200= (r+10)(t-1)    200=(10t-10+10)(t-1)  we have substituted r

anonymous · Answer

200=(10t)(t-1)     200=10t^2-10t     0=10t^2-10t-200   which we can factorise

anonymous · Answer

0=10(t^2-t-20)     0=t^2-t-20     0=(t-5)(t+4)   t=5  t=-4

anonymous · Answer

since time cannot be negative we take 5hrs

anonymous · Answer

now we find the speed =distance/time   =200/5=    40mil/hr