Discussion

A car travelling with 5/7th of its actual speed covers 42km in 1hr. 40mins. 48 secs. Find the actual speed of the car.

Answer: B

Convert the time to hours first.

\[ 1 \text{ h } 40 \text{ min } 48 \text{ s} = 1 + \frac{40}{60} + \frac{48}{3600} = 1.68 \text{ h} \]

\[ \text{reduced speed} = \frac{42}{1.68} = 25 \text{ km/hr} \]

That 25 is \( \tfrac{5}{7} \) of the actual speed:

\[ \frac{5}{7}v = 25 \quad\Longrightarrow\quad v = 35 \text{ km/hr} \]

Multiplying 25 by \( \tfrac{5}{7} \) instead of dividing gives \( 17\tfrac{6}{7} \) - the first distractor.

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