9. On level farmland, two runners leave at
the same time from the intersection of
two country roads. One runner jogs due
north at a constant rate of 8 miles per
hour while the second runner jogs due
east at a constant rate that is 4 miles per
hour faster than the first runner's rate.
How far apart, to the nearest mile, will
they be after
2
1 hour ?
(A) 6
(B) 7
(C) 8
(D) 12
(E) 14
north ---- 8mile/h, east ----12 miles/h, 1/2 hour ----- 4^2 + 6^2 = 根号 52, wrong ?
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