Question

a car travel at a speed of 40km/hr for DIStance of 20 km and the next of 20km with a speedof 60km/gr find the average speed

Answer 1

Answer:

The average speed will be: 48 km/h  

Step-by-step explanation:

FOR FIRST 20 KM

Distance covered by a car = 20 km

Speed at which the first 20 km distance was covered = 40 km/hr

• As we know time equals distance divided by speed.

So

Time taken to cover first 20 km distance= 20 ÷ 40 = 1 ÷ 2 hrs

FOR NEXT 20 KM

Distance  = 20 km

Speed at which the next 20 km distance was covered = 60 km/hr

Time taken to cover first 20 km distance = 20 ÷ 60 = 1 ÷3 hrs

so

Total time = Time taken to cover first 20 km distance + Time taken to cover first 20 km distance

                 $=\frac{1}{2}+\frac{1}{3}$

                 $=\frac{3}{6}+\frac{2}{6}$           ∵ $\mathrm{Least\:Common\:Multiplier\:of\:}2,\:3:\:\:6$

$\mathrm{Since\:the\:denominators\:are\:equal,\:combine\:the\:fractions}:\quad \frac{a}{c}\pm \frac{b}{c}=\frac{a\pm \:b}{c}$

                 $=\frac{3+2}{6}$

                 $=\frac{5}{6}$  

So total time = 5/6 hours

Thus,

average speed = $\left(20\:+\:20\right)\:\div \left(5\:\div \:6\right)$

                          $=\frac{40}{\frac{5}{6}}$

                          $=\frac{40\cdot \:6}{5}$         ∵ $\mathrm{Apply\:the\:fraction\:rule}:\:\frac{a}{\frac{b}{c}}=\frac{a\cdot \:\:c}{b}$

                          $=\frac{240}{5}$

                           $=48$ km/h

Therefore, the average speed will be: 48 km/h