A car completes a trip with an average speed of 50 mph. If the car covered 2/5 of the distance at 60 mph, what was the average speed for the remaining 3/5 of the distance?
Please help.
+130081 Call the total distance = D
The time for the first part of the trip = (2/5)D / 60 = D / 150
The time for the second part of the trip = (3/5)D / R where R is the rate we are looking for
And total distance / total time = avg rate
So
D / [ D/150 + (3/5)D / R ] = 50
1 / [ 1/150 + 3/ (5R) ] = 50
1 / [ R/ (150R) + 90 / (150R) ] = 50
150R / [ 90 +R ] = 50
3R / [ 90 + R ]= 1
3R = 90 + R
2R = 90
R = 45 mph
