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Question Number 207752 by efronzo1 last updated on 25/May/24

 Two ships have the same berth    in a port. It is known that the    arrival times of the two ships    are independent and have the    same probability of docking   on a Sunday (00.00−24.00)   If the berth time of the first ship   is 2 hours and the berth time   of the second ship is 4 hours,    the probability that one ship   will have to wait until the   berth can be used is    □ ((67)/(144))     □ ((67)/(288))    □ (1/4)    □((33)/(144))

Twoshipshavethesameberthinaport.ItisknownthatthearrivaltimesofthetwoshipsareindependentandhavethesameprobabilityofdockingonaSunday(00.0024.00)Iftheberthtimeofthefirstshipis2hoursandtheberthtimeofthesecondshipis4hours,theprobabilitythatoneshipwillhavetowaituntiltheberthcanbeusedis67144672881433144

Commented by mr W last updated on 25/May/24

p=1−((22^2 +20^2 )/(2×24^2 ))=((67)/(288)) ✓

p=1222+2022×242=67288

Commented by efronzo1 last updated on 25/May/24

why sir 1−((22^2 +24^2 )/(2.24^2 )) ?

whysir1222+2422.242?

Commented by mr W last updated on 25/May/24

my method see below

mymethodseebelow

Answered by mr W last updated on 25/May/24

Commented by mr W last updated on 25/May/24

say the first ship arrives at time x  (0≤x≤24) and the second ship at  time y (0≤y≤24).  such that the second ship doesn′t  need to wait:  y≥x+2     ...(i)  such that the first ship doesn′t  need to wait:  x≥y+4   ...(ii)  we can intepret this geometrically:  each point (x, y) in the square  24×24 shows the random arrival  times of both ships. if this point lies  in the hatched zones, which mean  the conditions (i) and (ii), then  no ship needs to wait. otherwise   one ship has to wait.  the area of hatched zones is  ((22^2 +20^2 )/2). the total area is 24^2 .  so the probability that one ship  has to wait is  p=((24^2 −((22^2 +20^2 )/2))/(24^2 ))=1−((22^2 +20^2 )/(2×24^2 ))=((67)/(288))

saythefirstshiparrivesattimex(0x24)andthesecondshipattimey(0y24).suchthatthesecondshipdoesntneedtowait:yx+2...(i)suchthatthefirstshipdoesntneedtowait:xy+4...(ii)wecanintepretthisgeometrically:eachpoint(x,y)inthesquare24×24showstherandomarrivaltimesofbothships.ifthispointliesinthehatchedzones,whichmeantheconditions(i)and(ii),thennoshipneedstowait.otherwiseoneshiphastowait.theareaofhatchedzonesis222+2022.thetotalareais242.sotheprobabilitythatoneshiphastowaitisp=242222+2022242=1222+2022×242=67288

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