How to cross the river with math problems, how to cross the river with math problems

1。The police first took the thief over, and then rowed back on their own, and there was only one thief opposite.

2。The police brought another son over and brought the thief back, and there was only one son on the other side.

3。The father took his sons over and rowed back by himself, and there were two sons opposite.

4。Dad took Mom over, Mom paddled back by herself, opposite Dad and his two sons.

5。The police took the thief with him, and the father rowed back, opposite the police thief and his two sons.

6。Dad and Mom went over together, Mom came back on her own, opposite the police thief Dad and his two sons.

7。Mom brought a daughter over, the police brought the thief back, opposite dad and two sons, mom also had a daughter.

8。The police brought a daughter over, and the police came back by themselves, opposite the father and two sons, the mother and the two daughters (the thief must be tied up, and he will slip away).

9。The police took the thief over, and everyone went to the other side!!

First of all, the police took the prisoners across the river, and the police came back and the prisoners stayed.

Then it was the police who took one of the father's sons across the river, the son stayed, and the police and the prisoners returned.

Then it was the dad who took the other son across the river, the son stayed, and the dad came back.

Then it was Dad who took Mom across the river, Mom came back and Dad stayed.

Then the police took the prisoners across the river, the police and the prisoners stayed, and Dad returned.

Then it was Dad who took Mom across the river, and Dad left Mom back.

Then it was the mother who took one of her daughters across the river, the mother and daughter stayed, and the police brought the prisoner back.

Then it was the police who took the mother's other daughter across the river, the daughter stayed, and the police returned.

Finally, it was the police who took the prisoners across the river. So they all crossed the river.

The first seven times were 7 people in the past and 1 person came back.

Forty-two people were transported in this way.

The remaining seven people passed for the eighth time.

So you need to carry seven rounds, plus the last eight, the total time is 3 7 2 + 3 = 45 seconds.

There is only one speedboat, which can seat 7 people, except for the driver, so 6 people are sent each time, 49 = 6 * 8 + 1

Another 6 seconds back and forth, except for the last one, so it takes 8*3*2-3=45 seconds to reach the other side of the river.

45 seconds.

In the first round, 7 people crossed the river and one person came back, 6 seconds.

In the second round, 6 seconds as above.

There are 7 rounds in total, and it takes 42 seconds. There are 42 people in the past, and there are 7 people left, once passed, 3 seconds. A total of 45 seconds.

？Does it take 3 seconds to cross the river each time is it one-way or two-way?

The answer for one-way is (49 7*2-1)*3=39, and the answer for two-way is 49 7*, right?

Bring the sheep back first, then the wolves.

Bring the sheep back after they have passed.

In the past with grass.

Finally in the sheep to go over.

First, take the pig across the river, unload the pig when it reaches the opposite bank, and return, the first round is over;

Take the dog the second time, unload the dog when you reach the opposite bank, bring the pig back, and the second round is over;

Bring a basket of vegetables for the third time, unload the vegetables after reaching the opposite bank, and return, and the third round is over;

The fourth time you just need to bring the pigs to the other side.

How to distribute Magic Math 4 to cross the river: 1. Take the mouse across the river 2, then take the cat across the river, put down the cat and bring the mouse that crossed the river first with the boat, put the mouse down 3, cross the river with only the rice 4, and then take the mouse across the river.

(1) Mom and Xiao Ming, Xiao Ming back 4

2) Grandpa and Grandma, Mom Back 15

3) Xiao Ming and Dad Xiao Ming Hui 7

3) Mom and Xiao Ming, 3

A total of 29 seconds, and in the end, Xiao Ming didn't have to reply.

Because it takes the least time to dismantle the rabbit, the rabbit is the "boatman", the rabbit takes three small animals across the river and comes back twice, the rabbit is equivalent to five one-way trips, and the rest of the animals are one-way. The time is 1*5+2+5+10=22