Question

On 800 km trip Ryan’s family travelled at 90 km/h for the first 600km and 100 km/h for the remainder of the journey. If they had travelled 90 km/h for the entire journey how much longer would the trip have taken

Answer 1

Choose whichever format you want to give the answer

`\boxed{(2)/(9) \textrm{ hour}}`

`\boxed{0.2222 \textrm{ hour}}`

`\boxed{13.3333 \textrm{ minutes}}`

Explanation:

`\sf{Travel\: time = (Distance)/(Speed)}`

The time taken to travel the first 600 km

`= (600)/(90) = (20)/(3)\; \sf{hours}`

This leaves 200 km which was travelled at a speed of 100 km/hr

Time taken for this stretch = 200/100 = 2 hours

If the entire trip were driven at 90 km/h, it would take the same time as the first case. Therefore we only need to be concerned about the last 200km

If the last 200km were traveled at 90 km/h instead of 100 km/h, time taken

`=(200)/(90) = (20)/(9)\\\\`

The difference in time then would be:

`=(20)/(9) - 2\\\\\\= (20)/(9) - (18)/(9)\\\\=(2)/(9)\; hour`

= 0.22 hour in decimal

= 13.33 minutes