Thread: average speed

Tom drove for 3 hours at 30 km/hr and another 2 hrs at 70km/h. What was his average speed for the journey?


attempt:

using S = d/t

Given: 2 hrs at 70km/h and 3 hrs at 30km/h

Solve: 30/3 + 70/2 = (10 + 35 ) /2 = 45/2 = 22.5 km/h

please correct me if im wrong.
because im not so sure with my solution.

thanks

Yes, you are wrong.
How far does he travel in the first 3 hours ?
How far does he travel in the next 2 hours ?
What is his total distance travelled ?
What is the total time taken ?
What is his average speed ?

Originally Posted by BobP

Yes, you are wrong.
How far does he travel in the first 3 hours ?
How far does he travel in the next 2 hours ?
What is his total distance travelled ?
What is the total time taken ?
What is his average speed ?

What was his average speed for the journey?

is only ask... but may i know how it is solved ...
thanks

Answer Bob's questions and you will have your answer.

3(30) + 2(70) = 90 + 140 = 230 km total
5 hrs also in total

230/5 = 46

so it is 46 km/hr is the answer..

can anyone check my solution because im so sure with my answer


thanks

Originally Posted by rcs

What was his average speed for the journey?

is only ask... but may i know how it is solved ...
thanks

By using the formula you wrote in your first post- average speed is the distance traveled divided by the time. And those are given by answering the questions in the first response.

how come and how it is really done?

Originally Posted by rcs

how come and how it is really done?

The equation for average speed is based on the total distance over the total time. So

-Dan

Originally Posted by rcs

3(30) + 2(70) = 90 + 140 = 230 km total
5 hrs also in total

230/5 = 46

so it is 46 km/hr is the answer..

can anyone check my solution because im so sure with my answer


thanks

This is correct.