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A car covers a distance in $$40$$ minutes with an average speed of $$60\ km$$ per hour. The average speed to cover the same distance in $$30$$ minutes is （ ）
A. $$80\ \frac{km}{h}$$
B. $$\frac {45}{2}\ \frac{km}{h}$$
C. $$70\ \frac{km}{h}$$
D. $$45\ \frac{km}{h}$$  Speed
00:00
03:11 ## QuestionMathsClass 8

A car covers a distance in $$40$$ minutes with an average speed of $$60\ km$$ per hour. The average speed to cover the same distance in $$30$$ minutes is （ ）
A. $$80\ \frac{km}{h}$$
B. $$\frac {45}{2}\ \frac{km}{h}$$
C. $$70\ \frac{km}{h}$$
D. $$45\ \frac{km}{h}$$

A
4.6     4.6     ## Solution

Given: Time = $$40$$ minutes = $$\frac{40}{60}=\frac23$$ hour, Speed =$$60\ km$$ per hour.
We know that, $$\text{Speed}=\frac{\text{Distance}}{\text{Time}}$$.
$$\therefore$$ Distance covered by a car = $$\text{Speed}\times\text{Time}$$$$=60\ \frac{km}{h}\times\frac{40}{60}\ h$$  [$$\because 1\ h=60$$ minutes]
$$=40\ km$$.
Now, the average speed to cover the same distance in $$30$$ minutes is,
$$\text{Speed}=\frac{\text{Distance}}{\text{Time}}$$
$$\Rightarrow \text{Speed}=\frac{40\ km}{\frac{30}{60}\ h}$$
$$=\frac{60\times40}{30}\ \frac{km}{h}$$
$$=2\times40\ \frac{km}{h}$$
$$=80\ \frac{km}{h}$$
Hence, the average speed to cover the same distance in $$30$$ minutes is $$80\ \frac{km}{h}$$.          