Question

A car travels 30 km at a uniform speed of 40km/h and the next 30 km at a uniform speed of 20km/h. Find its average speed.

Answer 1

average speed = distance travelled/time taken
1st time taken
= time = distance/ speed
time = 30/40
= 3/4 hour or 45 minutes
now 2nd time
= time = distance/speed
30/20 0r 90 mins
now distance travelled/time taken
(30 km + 20 km) / 3/4 + 3/2
= 50/9/4
average speed = 200/9 km/h



PLZ MARK IT AS BRAINLIST PLZ

Answer 2

$\huge\mathfrak{A{\underline{\underline{\textbf{\red{nswer :}}}}}}$

Average Speed = ?

$D_{1}$ (Distance) = 30 km

$S_{1}$ (Speed) = 40 km/hr.

$t_{1}$ (time) = $\dfrac{D1}{S1}$

$\dfrac{30}{40}$ => $\dfrac{3}{4}$

Similarly...

$D_{2}$ (Distance) = 30 km

$S_{2}$ (Speed) = 20 km/hr.

$t_{2}$ (time) = $\dfrac{D2}{S2}$

$\dfrac{30}{20}$ => $\dfrac{3}{2}$

Now... total time = $t_{1}$ + $t_{2}$

= $\dfrac{3}{4}\:+\:\dfrac{3}{2}$

= $\dfrac{6\:+\:3}{4}$

= $\dfrac{9}{4}$

= 2.25 hr.

Total distance = $D_{1}$ + $D_{2}$

= 30 + 30 = 60 km

Now..

Average Speed = $\dfrac{Total\: Distance}{Total\: time}$

= $\dfrac{60}{2.25}$

= 26.66 km/hr

$\boxed{\boxed{\textbf{Average Speed = 26.6 km/hr.}}}$

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