Question

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Answer 1

How long did it take to walk the first km, how long did it take to walk the second km?

Answer 2

You might want to answer in hours or fractions of an hour instead of minutes.

Answer 3

Then, average speed is total distance divided by total time.

Answer 4

No, it gives you enough information. How long did it take to walk the first km?

Answer 5

If it took one hour at 5 kmph, then the person would have walked 5 km.

But we just want the time to walk one km. So is it ten minutes (1/6 of an hour)? Thirty minutes (1/2 of an hour)?

Answer 6

Right, so 12 minutes or 1/5 of an hour to travel the first km.

Answer 7

What about the second km when we are going a little faster?

Answer 8

Close, it would be 1/7 of an hour or about 8 minutes and 34 seconds.

Answer 9

You can add 12 minutes plus 8 minutes and 34 seconds to get the total time or you can do it in fractions of an hour. Can you add the fractions 1/7 of an hour and 1/5 of an hour?

Answer 10

Finally you will take total distance (2 km) and divide by total time (in hours) to get average speed in kmph.

Answer 11

\[average=\frac{total -distance}{total-time}=\frac{1+1}{t_1+t_2}\\=\frac{1+1}{\frac{1}{5}+\frac{1}{7}}=\\\frac{2}{\frac{12}{35}}=\frac{70}{12}\]