1, your calculator
Our hands can also be calculators, which can do simple calculations. Give you a hint: when calculating the multiple of 9, count your fingers from left to right as shown in the figure. Now choose the multiple of 9 you want to calculate, assuming that the multiplication is 7×9. Bend the finger marked with the number 7 as shown. Then count the left index finger of the bent finger as 6, and the index of the left hand on its right is 3. Put them together, the answer of 7×9 is 63.
2. How many socks can you make a pair?
If you take out two socks, black and blue, from the drawer, they may never be a pair. But if you take out three socks from the drawer, no matter whether they are black or blue, you will end up with a pair of socks of the same color. In this way, with the help of one more sock, the mathematical rules can overcome Murphy's law.
Of course, this is only true if the socks are two colors. If there are blue, black and white socks in the drawer, take out a pair of socks with the same color, at least four pairs. If there are 10 pairs of socks with different colors in the drawer, you must take out 1 1 pairs of socks. According to the above situation, the mathematical rule is: if you have n kinds of socks, you must take out N+ 1 to ensure that a pair is exactly the same.
3. The problem of the train running in the opposite direction
The two trains run along the same track, both of which have a speed of 50 kilometers per hour. When the distance between two cars is100km, a fly flies from train A to train B at a speed of 60km/h.. After it meets the B train, it immediately turns around and flies to the A train, and so on until the two trains collide. How far did the fly fly before it was crushed to death? During the short time from the departure of the train to the collision, the fly kept flying at a speed of 60 kilometers per hour, so when the two cars collided, the fly flew 60 kilometers. So whether the fly flies in a straight line, along the "Z" line or rolls in the air, the result is the same.
4. Flipping a coin is not the fairest.
Flipping a coin is a common way to make a decision. People think this method is fair to both sides, because they think that the probability of coins falling upside down is the same as that of coins falling upside down, both of which are 50%. Interestingly, this very popular idea is not correct.
First of all, although it is unlikely that a coin will stand on the ground when it falls, this possibility exists. Secondly, even if this small possibility is ruled out, the test results show that if you flick the coin with your thumb in a conventional way, the probability that the coin will still be up when it hits the ground is about 5 1%.
The reason why this happens is that with a flick of the thumb, sometimes the money will not turn over, but will only rise like a trembling flying saucer and then fall. If the next time you want to choose which side of the coin in the hand of the coin thrower is facing up after landing, you should look at which side is facing up before throwing it, so that you have a greater chance of guessing correctly. But if that person is holding coins and turning his fists one by one, then you should choose the opposite from the beginning.
5. The probability of the same Amanome.
Suppose you are attending a wedding of 50 people, someone may ask, "I wonder what is the probability that two people here are in the same Amanome?" The same here refers to the same Amanome, for example, on May 5th, but it doesn't mean that the birth time is exactly the same. "
The correct answer is that about two guests whose birthdays are on the same day attend the wedding. If this group of people's birthdays are evenly distributed at any time of the year, then the probability that two people have the same birthday is 97%. In other words, you have to attend 30 parties of this size to meet a party without the same birthday.
The probability that two specific people are born at the same time is 1/365. The key to the problem is the size of the group. As the number of people increases, the probability that two people will be in the same Amanome will be higher. In a group of 10 people, the probability of two people in the same Amanome is about 12%. In a gathering of 50 people, the probability is about 97%. However, only when the number rises to 366 (one of whom may have been born on February 29th) can you be sure that the two people in this group must be the same Amanome.