Question

23. Kelvin travelled of his journey at 45 km/h and of the remaining journey at 90 km/h. The rest of his journey was completed in 1.2 h at an average speed of 100 km/h. What was the total time taken for the whole journey?​

Answer 1

4.6 hours

Explanation:

we first need to calculate the total distance he covered and total time taken whole for the journey.

Distance= speed X time

time = Distance/speed

let the total distance be X. he covers 2/5 if the journey first.

2/5 = 0.4

Time = 0.4x/45 hours

the remaining journey is 3/5x

he covers 1/3 X 3/5= 0.2x

time taken = 0.2/90 X hours

the remaining distance = 100× 1.2 = 120km

we add 0.4x + 0.2x to get the fraction he had covered

0.6x.

the remaining distance was X - 0.6x = 0.4 X

thus 120 km represents 0.4x of the journey

we calculate now the value of X

0.4x = 120

X = 300km

Total time taken = 0.4x/45 + 0.2/90 + 1.2 hours

replace X to get time

2.7 hours + 0.7 hours + 1.2 hours

= 4.6 hours