Question : A car completed a journey of 400 km in $12\frac{1}{2}$ hours. The first $\frac{3}{4}$th of the journey was done at 30 km/hr. Calculate the speed for the rest of the journey.
Option 1: 45 km/hr
Option 2: 25 km/hr
Option 3: 40 km/hr
Option 4: 30 km/hr
Correct Answer: 40 km/hr
Solution :
Total journey = 400 km
Speed of the car for $\frac{3}{4}$th journey = 30 km/hr
$\frac{3}{4}$th journey= $400\times(\frac{3}{4})$km = 300 km
Remaining journey = 400 – 300 = 100 km
Let the speed of the car for the rest of the journey be $x$ km/hr.
According to the question,
$\frac{300}{30}+\frac{100}{x}=\frac{25}{2}$
$⇒10+\frac{100}{x}=\frac{25}{2}$
$⇒x=100\times\frac{2}{5}$
$\therefore x= 40$ km/hr
Hence, the correct answer is 40 km/hr.
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