physics
posted by Jordan .
travelling at 90km/hr except for a 30 minute rest stop. Average speed for the trip is 78km/hr.
what is the total travelling time and what is the total distance travelled??
thanks

Let D = distance traveled (km)
T = total time of trip in hours
90 (T0.5) = D
D = 78 T
Two equations, two unknowns.
Solve by substitutuion.
90(T  0.5) = 78 T
12 T = 45
T = 3.75 hours (3.25 of which was driving)
D = 292.5 km