Question

Hola mate ❤

A person goes from point P to point Q covering 1/3 of the distance with speed 10km/hr . The next 1/3 of the distance at 20km/hr and the last 1/3 of the distance 60km/hr . The avearage speed of the person is

a) 30km/hr

b) 24 km/hr

c) 18 km/hr

d) 12km /hr

plzz solve it..​

Answer 1

Solution :

Let the total distance be 'x'.

Therefore,

$\sf{\frac{x}{3}}$ distance with 10 km/hr and then $\sf{\frac{x}{3}}$ distance with 20 km/hr and last $\sf{\frac{x}{3}}$ distance with 60 km/hr.

We know that,

Average speed:

$\implies$ $\boxed{\sf{V_{avg} = \frac{Total \: distance}{Total \: time}}}$

So, we get:

$\implies$ $\sf{V_{avg} = \frac{ \frac{x}{3} + \frac{x}{3} + \frac{x}{3} }{t1 + t2 + t3}}$

Now,

$\implies$ $\sf{t_{1} = \frac{ \frac{x}{3} }{10}}$

$\implies$ $\sf{t_{2} = \frac{ \frac{x}{3} }{20}}$

$\implies$ $\sf{t_{3} = \frac{ \frac{x}{3} }{60}}$

So,

$\implies$ $\sf{V_{avg} = \frac{ \frac{x}{3} + \frac{x}{3} + \frac{x}{3} }{ \frac{ \frac{x}{3} }{10} + \frac{ \frac{x}{3} }{20} + \frac{ \frac{x}{3} }{60} }}$

$\implies$ $\sf{V_{avg} = \frac{3}{ \frac{10}{60}} }$

$\implies$ $\sf{V_{avg }= 18 \: km/hr}$

Hence,

The average speed of the person is 18 km/hr.

Correct option: (c) 18 km/hr

____________________

Answered by: Niki Swar, Goa❤️

Answer 2

Answer:

time taken by the person from P to Q

10=1/3/t

10=1/3t

3t=1/10

t=1/30

the next

20=1/3/t

3t=1/20

t=1/60

the next

60=1/3/t

t=1/180

Average speed is equal to

total distance travelled by total time taken

so,

= ( 3×1/3)/(1/30+1/60+1/180)

=1/10/180

=18 km/hr

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