Question

What was the average speed if I drove 60 miles per hour to get to my grandmas house and 30 miles per hour to get home. Represent this in two different ways and explain your reasoning.

Answer 1

Answer:

40 mph.

Step-by-step explanation:

Suppose grandma's house is  30 miles away (any distance would do but 30 is convenient).

Speed = distance / time

time = distance / speed

Time to get there =  30/60 = 1/2 hour.

Time to get back = 30/30 = 1 hour

Average speed  = total distance/ total time

=  (30 + 30) / ( 1 + 1/2)

= 60 / 1.5

=  40 miles per hour.

You cannot take the average of the speeds directly

(60+ 30)/2  = 45 is not correct as you cannot average ratios ( speed is a ratio).