unitary math

Question

john's father starts off to drop john at his school 9.2 km away driving at 30 km/hr.After 4 minutes, jihn tells his father that he has to reach school in another 10 minutes.At what speed must john's father drive to reach the school at time

Answer 1

Good morning,

 

First calcualte how far did John's father drive in the first 4 minutes

 

30 km/60 minutes = x/4 minutes

 

cross multiply

 

x = 2 km

 

subtract that from 9.2 to see how far it then is to the school

 

his father needs to go 7.2 km in 10 minutes. What is that speed in km/hr?

 

7.2 km/10 minutes = x/60 minutes

 

cross multiply

 

x = 43.2 km/hr