A car drives a distance of d miles at 30 mph and returns at 60 mph. What is its average rate of the round trip?

# A car drives a distance of d miles at 30 mph and returns at 60 mph. What is its average rate of the round trip?

1. A
2. B
3. C
4. D

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### Solution:

Concept- We’ll assume the time taken by car reached a certain point and then return by taking a time of  ${t}_{1}$and ${t}_{2}$ hours respectively. We’ll use this formula
$\mathit{Time}=\frac{\mathit{distance}}{\mathit{speed}}$  to calculate time, and
$\mathit{Distance covered by the car}=\mathit{D miles}$
We know that,
$\mathit{time}=\frac{\mathit{distance}}{\mathit{speed}}$
Let ${t}_{1}$ be the time taken to reach the point.
${t}_{1}=\frac{d}{30}$
Let ${t}_{2}$ be the time taken to return the point.
${t}_{2}=\frac{d}{60}$
Let, $t$ total time taken to reach and to return to a certain point
$t={t}_{1}+{t}_{2}$
$t=\frac{d}{30}+\frac{d}{60}$
$t=\frac{2d+d}{60}$
$t=\frac{d}{20}$
$D=d+d$
$D=2d$

So,

Hence, the correct option is 3.

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