Question

Danielle drives from her home to the store at an average speed of 40 miles per hour. She returns home along the same route at an average of 60 miles per hour. What is her average speed, in miles per hour, for the entire trip

Answer 1

she drove 40 mph & 60 mph

60 +40 = 100

100/2 = 50

 so she drove an average of 50 mph

Answer 2

Danielle average speed for the entire trip is equals to 48miles per hour.

What is average speed?

" Average speed is defined as ratio of the total distance travelled to the total time taken."

Formula used

Average speed = (Total distance travelled) / (total time taken)

Time = (distance travelled )/ (average speed)

According to the question,

Let 'D' be the distance between her home to the store.

Time taken to drive from her home to the store = t₁

Time taken to drive from her store to the home = t₂

Average speed from her home to the store = 40 miles per hour

Average speed from her store to the home = 60 miles per hour

Substitute the value in the formula to get the time taken for each average speed,

t₁ = $\frac{D}{40}$

t₂ = $\frac{D}{60}$

Substitute the value in the formula to get the average speed for the entire trip,

Average speed = $\frac{D +D}{\frac{D}{40} +\frac{D}{60} }$

                          $= \frac{2D}{\frac{60D+40D}{(60)(40)} }$

                          $= \frac{2(60)(40)}{100}$

                         $= 48$ miles per hour

Hence, average speed for the entire trip is equals to 48miles per hour

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