Question 999955
Let x be the speed at 100 km/h
y be speed at 50 km/h

total distance = 1000 km
d=rt

100x+50y = 1000

time
x+y = 12.3 
multiply bu 100
100x + 100y = 1230
subtract the equations0y = 230
y= 4.6

distance at 50 km/h = 4.6 * 50 = 230km

7.7 hours at 100 km/h = 770 km