andre drove part of a 260km trip at 80kph and the rest at 100kph. find the distance he traveled at 80kph if his total driving time was 2h 30min
let the distance traveled at the slower speed be x km
distance at faster speed = 260-x
time at slower = x/80
time at faster =(260-x)/100
x/80 + (260-x)/100 = 2.5
multiply by 400
5x + 4(260-x) = 1000
5x + 1050 - 4x = 1000
x = -50
not possible, no solution
(should be obvious from the start,
even if he had gone the entire trip at the faster speed of 100 km/h, it would take him 260/100 hrs or 2.6 hrs)