SOLUTION: sam drove 500km from city A to City B in 5.5hr. he drove part of the way at 100km/h and the rest of the way at 80km/h. how far did he drive at each speed?

Question 332717: sam drove 500km from city A to City B in 5.5hr. he drove part of the way at 100km/h and the rest of the way at 80km/h. how far did he drive at each speed?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
total distance = 500 km
..
he drove x km at 100 km/h
500-x at 80 km/h
..
time he drove at 100 = x/100
time he drove at 80 = (500-x)/ 80
..
total time he drove = 5.5 hours = 11/2 hours
..
x/100+(500-x)/80 = 11/2
8x+10(500-x) / 800 = 11/2
8x+5000-10x / 800 = 11/2
-2x+5000 / 800 = 11/2
2(-2x+5000)= 11*800
-4x+10000=8800
-4x=-10000+8800
-4x=-1200
x=-1200/-4
x=300 km. the distance he drove at 100km/h
Balance 200 km he drove at 80 km/h
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