what is the average speed

Question

Padre drives 2 hours  at average speed of 35 miles per hour.  Then she drives 3 hours at a speed of 48 miles per hour. What is her average speed of the whole trip 

Answer 1

Okay, so I would break this down into two steps.  First, she drives 35mph for two hours.  So, she has driven 70 miles in the first two hours.

 

Secondly, she drives 48mph for three hours.  So, she has driven 48x3 miles in the three hours. This means she has driven 144 miles in the 3 hours.

 

Finally, add them together.  She has driven (144 +70) miles in (2+3) hours. In other words, she has driven 214 miles in 5 hours. 

 

To find the average, we divide 214 by 5.  214/5 = 42.8mph