John drove 720 km between City A and City B. (a) He took (x-30) minutes to travel the first 400 km at a constant speed. Write down an expression, in terms of x, for the speed in km/h for the first 400 km. [1] (b) John took x minutes to travel the rest of the journey at a different constant speed. His speed for the first part of the journey was 30 km/h faster than for the second part. Write down an equation in x to represent this information, and show that it reduces to x²-190x-19200 = 0. [3] (c) Solve the equation x²-190x-19200 = 0, giving your solutions correct to three significant figures. [3] (d) Calculate John's average speed, in km/h, for the whole journey. [2]
