TedTest

From the Ted Talk by Lisa Winer: Can you solve the river crossing riddle?

Unscramble the Blue Letters

As a wlirfide rages through the grasslands, three lions and three wildebeest flee for their lives. To escape the inferno, they must cross over to the left bank of a crocodile-infested river. Fortunately, there happens to be a raft nrabey. It can carry up to two aliamns at a time, and needs as least one lion or wildebeest on board to row it across the river. There's just one problem. If the lions ever outnumber the wildebeest on either side of the river, even for a moment, their instincts will kick in, and the results won't be pretty. That inlcedus the animals in the boat when it's on a given side of the rvier. What's the fastest way for all six animals to get across without the lions stopping for dinner? Pause here if you want to figure it out for yourself. Answer in: 3 Answer in: 2 aswenr in: 1 If you feel stuck on a problem like this, try listing all the doscnieis you can make at each point, and the cenceqoeusns each choice leads to. For ictnanse, there are five options for who goes across first: one wildebeest, one lion, two wildebeest, two lions, or one of each. If one aimanl goes alone, it'll just have to come straight back. And if two wileeedbst cosrs first, the remaining one will immediately get eaten. So those options are all out. Sending two lions, or one of each animal, can actually both lead to solutions in the same number of moves. For the sake of time, we'll focus on the second one. One of each animal crosses. Now, if the wildebeest stays and the lion returns, there will be three lions on the right bank. Bad news for the two remaining wildebeest. So we need to have the lion stay on the left bank and the wildebeest go back to the right. Now we have the same five options, but with one lion already on the left bank. If two wildebeest go, the one that stays will get eaten, and if one of each animal goes, the wildebeest on the raft will be obetreunmud as soon as it rceeahs the other side. So that's a dead end, which means that at the third crossing, only the two lions can go. One gets dropped off, leaving two lonis on the left bank. The third lion teaks the raft back to the right bank where the wildebeest are waiting. What now? Well, since we've got two lions waiting on the left bank, the only option is for two wildebeest to cross. Next, there's no sense in two wildebeest going back, since that just reverses the last step. And if two lions go back, they'll outnumber the wildebeest on the right bank. So one lion and one wildebeest take the raft back lnaievg us with one of each animal on the left bank and two of each on the right. Again, there's no point in sedning the lion-wildebeest pair back, so the next trip should be either a pair of lions or a pair of wildebeest. If the lions go, they'd eat the wildebeest on the left, so they stay, and the two wildebeest cross instead. Now we're quite colse because the wildebeest are all where they need to be with sfetay in numbers. All that's left is for that one lion to raft back and bring his fellow lions over one by one. That makes eleven trips total, the smallest number needed to get everyone across safely. The solution that ilnevovs sending both lions on the first step wokrs similarly, and also takes eveeln crossings. The six animals escape unharmed from the fire just in time and begin their new lives across the river. Of course, now that the danger's passed, it remains to be seen how long their unlikely alliance will last.

Open Cloze

As a ________ rages through the grasslands, three lions and three wildebeest flee for their lives. To escape the inferno, they must cross over to the left bank of a crocodile-infested river. Fortunately, there happens to be a raft ______. It can carry up to two _______ at a time, and needs as least one lion or wildebeest on board to row it across the river. There's just one problem. If the lions ever outnumber the wildebeest on either side of the river, even for a moment, their instincts will kick in, and the results won't be pretty. That ________ the animals in the boat when it's on a given side of the _____. What's the fastest way for all six animals to get across without the lions stopping for dinner? Pause here if you want to figure it out for yourself. Answer in: 3 Answer in: 2 ______ in: 1 If you feel stuck on a problem like this, try listing all the _________ you can make at each point, and the ____________ each choice leads to. For ________, there are five options for who goes across first: one wildebeest, one lion, two wildebeest, two lions, or one of each. If one ______ goes alone, it'll just have to come straight back. And if two __________ _____ first, the remaining one will immediately get eaten. So those options are all out. Sending two lions, or one of each animal, can actually both lead to solutions in the same number of moves. For the sake of time, we'll focus on the second one. One of each animal crosses. Now, if the wildebeest stays and the lion returns, there will be three lions on the right bank. Bad news for the two remaining wildebeest. So we need to have the lion stay on the left bank and the wildebeest go back to the right. Now we have the same five options, but with one lion already on the left bank. If two wildebeest go, the one that stays will get eaten, and if one of each animal goes, the wildebeest on the raft will be ___________ as soon as it _______ the other side. So that's a dead end, which means that at the third crossing, only the two lions can go. One gets dropped off, leaving two _____ on the left bank. The third lion _____ the raft back to the right bank where the wildebeest are waiting. What now? Well, since we've got two lions waiting on the left bank, the only option is for two wildebeest to cross. Next, there's no sense in two wildebeest going back, since that just reverses the last step. And if two lions go back, they'll outnumber the wildebeest on the right bank. So one lion and one wildebeest take the raft back _______ us with one of each animal on the left bank and two of each on the right. Again, there's no point in _______ the lion-wildebeest pair back, so the next trip should be either a pair of lions or a pair of wildebeest. If the lions go, they'd eat the wildebeest on the left, so they stay, and the two wildebeest cross instead. Now we're quite _____ because the wildebeest are all where they need to be with ______ in numbers. All that's left is for that one lion to raft back and bring his fellow lions over one by one. That makes eleven trips total, the smallest number needed to get everyone across safely. The solution that ________ sending both lions on the first step _____ similarly, and also takes ______ crossings. The six animals escape unharmed from the fire just in time and begin their new lives across the river. Of course, now that the danger's passed, it remains to be seen how long their unlikely alliance will last.

Solution

eleven
outnumbered
involves
answer
takes
wildfire
safety
animal
cross
leaving
reaches
close
decisions
works
nearby
animals
wildebeest
river
includes
instance
sending
lions
consequences

Original Text

As a wildfire rages through the grasslands, three lions and three wildebeest flee for their lives. To escape the inferno, they must cross over to the left bank of a crocodile-infested river. Fortunately, there happens to be a raft nearby. It can carry up to two animals at a time, and needs as least one lion or wildebeest on board to row it across the river. There's just one problem. If the lions ever outnumber the wildebeest on either side of the river, even for a moment, their instincts will kick in, and the results won't be pretty. That includes the animals in the boat when it's on a given side of the river. What's the fastest way for all six animals to get across without the lions stopping for dinner? Pause here if you want to figure it out for yourself. Answer in: 3 Answer in: 2 Answer in: 1 If you feel stuck on a problem like this, try listing all the decisions you can make at each point, and the consequences each choice leads to. For instance, there are five options for who goes across first: one wildebeest, one lion, two wildebeest, two lions, or one of each. If one animal goes alone, it'll just have to come straight back. And if two wildebeest cross first, the remaining one will immediately get eaten. So those options are all out. Sending two lions, or one of each animal, can actually both lead to solutions in the same number of moves. For the sake of time, we'll focus on the second one. One of each animal crosses. Now, if the wildebeest stays and the lion returns, there will be three lions on the right bank. Bad news for the two remaining wildebeest. So we need to have the lion stay on the left bank and the wildebeest go back to the right. Now we have the same five options, but with one lion already on the left bank. If two wildebeest go, the one that stays will get eaten, and if one of each animal goes, the wildebeest on the raft will be outnumbered as soon as it reaches the other side. So that's a dead end, which means that at the third crossing, only the two lions can go. One gets dropped off, leaving two lions on the left bank. The third lion takes the raft back to the right bank where the wildebeest are waiting. What now? Well, since we've got two lions waiting on the left bank, the only option is for two wildebeest to cross. Next, there's no sense in two wildebeest going back, since that just reverses the last step. And if two lions go back, they'll outnumber the wildebeest on the right bank. So one lion and one wildebeest take the raft back leaving us with one of each animal on the left bank and two of each on the right. Again, there's no point in sending the lion-wildebeest pair back, so the next trip should be either a pair of lions or a pair of wildebeest. If the lions go, they'd eat the wildebeest on the left, so they stay, and the two wildebeest cross instead. Now we're quite close because the wildebeest are all where they need to be with safety in numbers. All that's left is for that one lion to raft back and bring his fellow lions over one by one. That makes eleven trips total, the smallest number needed to get everyone across safely. The solution that involves sending both lions on the first step works similarly, and also takes eleven crossings. The six animals escape unharmed from the fire just in time and begin their new lives across the river. Of course, now that the danger's passed, it remains to be seen how long their unlikely alliance will last.

Frequently Occurring Word Combinations

ngrams of length 2

collocation	frequency
left bank	5
wildebeest cross	2

Important Words

alliance
animal
animals
answer
bad
bank
board
boat
bring
carry
choice
close
consequences
cross
crosses
crossing
crossings
dead
decisions
dinner
dropped
eat
eaten
eleven
escape
fastest
feel
fellow
figure
fire
flee
focus
fortunately
grasslands
immediately
includes
inferno
instance
instincts
involves
kick
lead
leads
leaving
left
lion
lions
listing
lives
long
means
moment
moves
nearby
needed
news
number
numbers
option
options
outnumber
outnumbered
pair
passed
pause
point
pretty
problem
raft
rages
reaches
remaining
remains
results
returns
reverses
river
row
safely
safety
sake
sending
sense
side
similarly
smallest
solution
solutions
stay
stays
step
stopping
straight
stuck
takes
time
total
trip
trips
unharmed
waiting
wildebeest
wildfire
works