Question

A girl decides to go for shopping. The mall is 5 km from her home. She covers the first 3 km at a speed of 30 km/hr. She is stuck in traffic for 6 minutes and covers rest of the distance at 40 km/hr. How much time did she take to reach the mall? Also, find her average speed. [5 MARKS]

Answer 1

Total Time: 2 Marks
Average speed: 1 Mark
Formula: 1 Mark
Steps: 1 Mark

Time taken to cover first 3 km $=\frac{3}{30}=\frac{1}{10}hr$

Time taken to cover last 2 km $=\frac{2}{40}=\frac{1}{20}hr$

Time she was stuck in traffic = 6 min $=\frac{6}{60}=\frac{1}{10}hr$

Total time taken $=\frac{1}{10}+\frac{1}{20}+\frac{1}{10}=\frac{5}{20}=\frac{1}{4}hr$ = 15 minutes

Now, Average Speed $=\frac{TotalDistance}{TotalTime}$
$=\frac{5}{0.25}$
=20 km/hr