Question : A car left 3 minutes earlier than the scheduled time and to reach the destination 126 km away in time, it has to slow its speed by 6 km/hr from the usual. What is the usual speed (in km/hr) of the car?
Option 1: 56
Option 2: 63
Option 3: 94.5
Option 4: 126
Correct Answer: 126
Solution : Let the usual speed be $x$ km/hr. According to the question, $\frac{126}{x}-\frac{126}{x-6}=\frac{3}{60}$ $⇒\frac{252}{x^2-6x}=\frac{1}{60}$ $⇒x^2-6x-15120=0$ $⇒x^2-(126-120)x-15120=0$ $⇒(x-126)(x+120)=0$ As speed can't be negative, $\therefore x= 126$ km/hr Hence, the correct answer is 126.
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