Question 905379: During his semester break, Zack went on a road trip from Berlin to Prague. He travelled part of the journey at a speed of 90 km/h and the rest at 80 km/h. Given that Zack travelled a total distcance of 690 km in 8 hours, form a pair of simultaneous equations to find the distance that he covered at 80 km/h.
Answer by ankor@dixie-net.com(22740)   (Show Source):
You can put this solution on YOUR website! He travelled part of the journey at a speed of 90 km/h and the rest at 80 km/h.
Given that Zack travelled a total distance of 690 km in 8 hours, form a pair of simultaneous equations to find the distance that he covered at 80 km/h.
:
let x = time at 80 km/hr
let y = time at 90
:
x + y = 8
and
80x + 90y = 690
Simplify, divide eq by 10
8x + 9y = 69
:
Multiply the 1st equation by 9, subtract the above equation
9x + 9y = 72
8x + 9y = 69
--------------Subtractions eliminates y, find x
x = 3 hrs at 80 km/hr
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:
I'll let you confirm this, find y and check these values for x and y in both original equations
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