Answer:
A
Step-by-step explanation:
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P(at least 5 rolls until 1) = P(4 rolls are not 1) = 5/6 x 5/6 x 5/6 x 5/6 = 0.4823 (4sf)
Fewer than 7 rolls to get second 1 after first takes 3 rolls means second occurs on 4th, 5th or 6th roll
The probability of each of these is 1/6, 5/6 x 1/6 and 5/6 x 5/6 x 1/6 respectively.
P(second 1 on 4th, 5th or 6th roll) = 1/6 + 5/36 + 25/216 = 91/216 = 0.4213 (4sf)
Distance = 30 mph * time
distance = 4 mph * time
distance = 30 mph * t
distance = 4 mph * (17-t)
Since distance is equal then
30 mph * t = 4 mph * (17-t)
30t = -4t + 68
34t = 68
t = 2 hours
We see the return trip time is (17 -t ) which is 15 hours.
The beginning trip time is 2 hours.
Double Check
Beginning trip = 30 miles * 2 = 60 miles
Return trip = 4 miles * 15 = 60 miles.
