Question

a bike crosses 21 poles in a minutes time the distance between two consecutive poles is 40 m.find the average speed in km/h

Answer 1

So crosses 20 poles.
Therefore distance = 40×20=800m
Time=1min= 60sec

Speed=800/60= 80/6 m/s
In km/h= 80×18/6×5
= 16×3/1
= 48 km/h.

Pls mark as BRAINLIEST

Answer 2

Given:

Number of poles crossed by a bike in a minute = 21

Distance between two consecutive poles = 40 m.

To find:

Average speed of bike in km/h

Solution:

Distance between two consecutive poles = 40 m

So, distance between three consecutive poles = 40 + 40 = 80 m

Distance between 5 consecutive poles = 4 $\times$ 40 = 160 m

{As, observing the pattern,

Distance between n poles = (n-1) $\times$ Distance between two consecutive poles}

Thus, distance between 21 consecutive poles = 20 $\times$ 40 = 800 m

Since we know, Speed = $\dfrac{Distance}{Time}$

Distance = 800 m = 800 $\div$ 1000 km {As 1 km = 1000 m}

               = 0.8 km

Time = 1 minute = 1 $\div$ 60 hours {As 1 hour = 60 minutes}

         = 0.0167 h

Putting the values, we get:

Thus, Speed = $\frac{0.8}{0.0167} =$ 47.9 km/h

$\therefore$ Average speed of bike in km/h = 47.9 km/h