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Elizabeth visits her friend Andrew and then returns home by the same route. She always walks 2km/h when going uphill, 6km/h when going downhill and 3km/h when on level ground. If her total walking time is 6 hours, then what is the total distance she walks in km?
She walks 18km in total.

using u,d,f for uphill, downhill, flat distances on the outward journey,

recall that time = distance/speed

she walks 9 km in each direction

(u/2 + f/3 + d/6) + (d/2 + f/3 + u/6) = 6
2u/3 + 2f/3 + 2d/3 = 6
u + f + d = 9

you are correct. the round trip is 18 km.

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