im not good at explaining. But here goes....
first find her average speed of the combined uphill and downhill journey.
Total hours she walk : 5
Flat slope : 4km/h
Upslope: 3km/h
Downslope : 6km/h
the problem is we dunno how much distance is upslope and downslope. but one thing we know she walked back the same route home. that means whatever distance she walk upslope, on the return trip, she walk downslope.
now let the slopping distance be Z km.
when she walk upslope, she used Z/3 hours. then downslope is Z/6 hours, same idea.
she walked the slopping distance 2 times, so she walked 2(Z) km of slope, upslope and downslope.
so average speed of all slopes is (total distance) / (total time)
total distance is 2 (Z) km
total time is (Z/3) hours + (Z/6) hours
So solution?
total time is 1/3( Z) hours + 1/6 ( Z) hours
which is 2/6 + 1/6 = 3/6 = 1/2 (Z) hours.
So total time is 1/2(Z) hours.
Now let's find average speed. Total distance / total time. The slope is Z km long.
She walked a Z km long sloping road 2 times.
So its 2(Z) km
Total Time : 1/2 (Z) hours
Divide total distance by total time
2( Z) km divide by 1/2( Z) hours
So the answer is 4km/hr
So average speed is 4km/hr. Z got cancelled already because both the distance and time contains Z.
her average speed on slope is 4km/h.
her speed on flat road is also 4km/h.'
So? Overall Speed is 4km/h.
She walks from 7 to 12 which is 5 hrs.
So answer for the question is..... 4km/hr times 5hrs which is 20 km
Answer is 20 km!!
Hope you got it....
