Question 1043631
The trail is x km long
at kx, k <1, there is 10 km left, so x-kx=10.
x(1-k)=10.
x=10/(1-k)
Because this is per cent for k, everything has to be multiplied by 100.
1000/(100-k) would be the answer.
D
Check
Suppose the trail is 25 km long, and she has 10 km left.  She has walked 60 per cent of the trail
1000/(100-60)=1000/40=25 km.
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If she had walked 20% of the trail and had 10 km left
1000/(100-20)=12.5 km.  That would mean she had walked 2.5 km (1/5 of 12.5 or 20%) and had 10 km left.