SOLUTION: a motorist travels for 1hr at an average speed of 72km/h and then for 2hrs at a average speed of 90km/h calculate his average speed for the whole journey.

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Question 677239: a motorist travels for 1hr at an average speed of 72km/h and then for 2hrs at a average speed of 90km/h calculate his average speed for the whole journey.
Answer by checkley79(3341) About Me  (Show Source):
You can put this solution on YOUR website!
D=RT
D=72*1=72 KM.
D=90*2=180 KM.
72+180=252 TOTAL KM.
1+2=3 TOTAL HOURS.
252=R*3
R=252/3
R=84 KM. IS THE AVERAGE SPEED.