Question

A car travelling with $\frac{5}{7}$ of its usual speed covers $42$ km in $1$ hour $40$ mins $48$ sec. What is the usual speed of the car?

• A. $17\frac{6}{7}km/hr$
• B. $25km/hr$
• C. $30km/hr$
• D. $35km/hr$

Answer 1

The correct option is D $35km/hr$

To find the usual speed of the car

Here , Total time is 1 hour 40 mins 48 sec

$T=1+\frac{40}{60}hr+\frac{48}{3600}hr$

$T=1+\frac{2}{3}hr+\frac{1}{75}hr$

$T=\frac{126}{75}hr$

Here, distance $=42km$

As we know that

$Speed=\frac{Distance}{Time}$

$Speed=\frac{42}{\frac{126}{75}}$

$Speed=\frac{42\times 75}{126}km/hr$

$Speed=25Km/hr$

Now, $\frac{5}{7}$ of the Actual speed = $25$ Km/hr

Actual Speed $=25\times \frac{7}{5}=35Km/hr$

Hence, Option D is correct.