## chris215 one year ago -

1. Valpey

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

2. Valpey

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

3. Valpey

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

4. Valpey

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

5. Valpey

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)?

6. Valpey

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

7. Valpey

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

8. Valpey

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

9. Valpey

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?

10. Valpey

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

11. amoodarya

|dw:1435698025138:dw|$average=\frac{total -distance}{total-time}=\frac{1+1}{t_1+t_2}\\=\frac{1+1}{\frac{1}{5}+\frac{1}{7}}=\\\frac{2}{\frac{12}{35}}=\frac{70}{12}$

12. Valpey

You got it