Joe took 12 minutes to drive 9 km. At this speed, how many km could he drive in 3 hours?

Question

I would like to know the simplest way to work this out step by step :)

Answer 1

This is a D-I-R-T (Distance-Is-Rate-times-Time) problem.  We only have to convert units using the Multiplicative Identity (that is, 1).  Note that the problem asks for time in hours, so we convert minutes to hours.

 

    Distance(how far?) =            Rate   *       Time

               D  = ((9 km)/(12 minutes)) * (3 hours)

               D  = ((9 km)/(12 min))*((60 min)/(1 hr)) * (3 hr)

               D  = (9/12)(60)(3) km/hr     [note: min and hr cancel out; leaving only km]

               D = 135 km

 

Answer 2

3 hours = 180 minutes

 

Using a proportion

 

9 km / 12 min = x km / 180      multiply both sides by 180

180(9 km) / 12 = x km              divide

15(9km) = x km                        multiply

135 km = x km

 

You can drive 135 km in three hours.