Question

a bus traveling the first one third distance at a speed 15 km/h the nextone third at 20 km/h and the last one third at 40 km/h .the average speed of bus is​

Answer 1

(15+20+40)/3=75/3=25 km/h

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Answer 2

${\huge{\boxed{\mathcal{\red{Answer}}}}}$

25km/h

${\huge{\boxed{\mathcal{\red{Explanation}}}}}$

Let the total distance travelled by bus be x m.

Now it is given :

It travels distance = x/3

speed = 15km/h

$in \: time \: = t_1$

Again it travels = x/3

speed = 20km/h

$in \: time = t_2$

Again it travels = x/3

speed = 40km/h

$in \: time = t_3$

Now in the total journey the total time taken to travel :

$t_1 + t_2 + t_3$

And the total distance =x

Now :

$t_1 = dis \div speed$

$t_1 = \frac{ \frac{x}{3} }{15}$

$t_1 = \frac{15x}{3}$

Similarly time in all cases will be

$t_2 = \frac{ \frac{x}{3} }{20}$

$t_2 = \frac{20x}{3}$

Time in third case :

$t_3 = \frac{ \frac{x}{3} }{40}$

$t_3 = \frac{40x}{3}$

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Now average speed of bus is = total distance travelled / total time taken.

Thus we get average speed of bus is :

$\frac{x}{ \frac{15x}{3} + \frac{20x}{3} + \frac{4 0x }{3} }$

$= \frac{x}{ \frac{75x}{3} }$

$= \frac{75}{3}$

$= 25$

Thus average speed of bus is 25km/h

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BY SCIVIBHANSHU

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