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

The average speed will be: 48 km/h

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

`=(1)/(2)+(1)/(3)`

`=(3)/(6)+(2)/(6)` ∵
`\mathrm{Least\:Common\:Multiplier\:of\:}2,\:3:\:\:6`

`\mathrm{Since\:the\:denominators\:are\:equal,\:combine\:the\:fractions}:\quad (a)/(c)\pm (b)/(c)=(a\pm \:b)/(c)`

`=(3+2)/(6)`

`=(5)/(6)`

So total time = 5/6 hours

Thus,

average speed =
`\left(20\:+\:20\right)\:/ \left(5\:/ \:6\right)`

`=(40)/((5)/(6))`

`=(40\cdot \:6)/(5)` ∵
`\mathrm{Apply\:the\:fraction\:rule}:\:(a)/((b)/(c))=(a\cdot \:\:c)/(b)`

`=(240)/(5)`

`=48` km/h

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