1. logic question

On the M53 is a sign Warington 20. Just over half a mile further on is another sign ‘Warrington 19’. This is not surprising, since the distance are rounded to the nearest while number of miles e.g numbers of 4.5 and over but less than 5 become 5, numbers of 4 and over but less than 4.5 become 4. Half a mile further along the road is a sign showing ‘Warrington 18’.
The distance must now be btwen ?

A) 17.5 miles and 17.6 miles
B) 17.6 miles and 18.0 miles
C) 18.0 miles and 18.2 miles
D) 18.2 miles and 18.4 miles
E) 18.4 miles and 18.5 miles

My attempt :

Warrington ---- W 20 ---- W 19 ------W 18

Distance of W 20 from Warrington can be 19.5 - 20.0 . Then W 19 is more than half a mile from W 20 .. How much can it be ??

2. Distance of W 20 from Warrington can be 19.5–20.5. "Just over half a mile further on" (call it 0.6 miles), that will have come down to 18.9–19.9. But the sign says 19, so in fact it must be 18.9–19.5. Half a mile further on, that will have come down to 18.4–19.0. But the sign says 18, so in fact it must be 18.4–18.5.