Between two points, a car accelerates uniformly at first, then moves with constant speed and finally retards uniformly to rest. If the ratio of time takes is `1:4:2` and the maximum speed is `70 km//h`, find the average speed over the whole journey.

Explanation

To find the average speed of the car over the entire journey, we will break the problem down into steps based on the information provided.

### Step 1: Understand the time ratio and total time
The car accelerates, moves at constant speed, and then decelerates. The time ratios for these three phases are given as 1:4:2.

Let the time taken for acceleration be \( t_1 = x \), for constant speed be \( t_2 = 4x \), and for deceleration be \( t_3 = 2x \).

The total time \( T \) for the journey is:
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