Robin drove part of a 260 km trip at 80 kilometers per hour

Robin drove part of a 260 km trip at 80 kilometers per hour and the rest at 100 km/hr. Find the distance he traveled at 80 km/hr if his total driving time was 2 hours and 30 minutes.

Solution

Let ur assume, he covered X distance at 80 kmph.

Hence, remaining distance 260-X covered at 100 kmph.

Time required to cover X distance at 80 kmph = X/80

Time required to cover X distance at 80 kmph = 260-X/100

Total time =  [X/80 ]+ [260-X/100]

But, given that total time = 2 hours and 30 minutes = 2.5 hrs

Then,

[X/80]+ [260-X/100] = 2.5

10X + 2080-8X = 2000

X = -40 km

Therefore,

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