Interesting math problem is a popular intellectual entertainment activity using math knowledge. In order to increase interest, interesting math problems are often expressed in more complicated or very life-like ways. The following are interesting questions about the fourth grade mathematics in primary school. I hope everyone will read it carefully!
Flies and bicycles
Math brain teaser: Two boys each ride a bicycle and ride in a straight line from two places 20 miles apart. At the moment they set off, a fly on the handlebar of one bicycle began to fly straight to another bicycle. As soon as it touched the handlebar of another bicycle, it immediately turned around and flew back. The fly shuttled back and forth between the handlebars of two bicycles until they met. If each bicycle moves at a constant speed of 10 miles per hour and flies fly at a constant speed of 15 miles per hour, how many miles will flies fly?
Answer: The speed of each bicycle is 10 miles per hour. 1 hour later, the two cars met at the midpoint of the distance of 20 miles. The speed of flies is 15 miles per hour, so they fly in 1 hour 15 miles. It's that simple! Many people try to calculate the first distance between the handlebars of two bicycles, then return the distance, and so on to calculate those shorter and shorter distances. But this will involve the so-called infinite series summation, so it is very complicated.
The son, daughter and wife divide the property skillfully.
Math brain teaser: There is a very rich family. The husband suddenly got an incurable disease. Leave a will before you die? If the wife gives birth to a boy, the wife and son share half of the property. If it is a girl, the girl gets one-third of the property and the rest goes to the wife. ? Shortly after her husband died, her wife was going to give birth. Unexpectedly, my wife gave birth to a boy and a girl twins! Now the wife is in a dilemma: how to divide this property?
Answer: The key here is not quantity, but quantity relationship. Careful analysis of the will shows that the number of wives and sons is the same, and the number of wives is twice that of daughters. With this relationship, it is not difficult to distribute: the wife and son each get two-fifths and the daughter gets one-fifth.
Infantry crossing the bridge
Math brain teaser: There are 692 infantry in a fortress. Every four people stand in a horizontal row, walk forward at intervals of 1 meter 1, and walk 86 meters per minute. Now we must cross this 86-meter-long bridge. How many minutes does it take from the first row to the last row?
Answer: 3 minutes.
A chess game with 12 participants.
Math brain teaser: China Chess Competition was held in the sixth grade, and 12 people signed up for the competition. According to the rules of the game, everyone has to play a game of chess with others, so how many games will this game be played?
Answer: One * * * can play 66 sets. If we want to get the right answer, we can simply think of it and see what the rules are. If two people (A and B) take part in the competition, 1 set is enough for the competition; If three people (a, b, c) take part in the competition, then a? b、A？ c、B？ C wants to play 3 sets; If four people take part in the competition and need six sets, you can find that two people take part in the competition and need 1 set, that is, 1 set; 3 people take part in the competition, which requires 3 sets, namely12; 4 entries and 6 groups, namely123; Five people participated in the competition, playing 10 sets, namely1234; Then, 12 people will compete in 1 2 3 1 1=66 sets.
You can also think of it this way: each of these 12 people will play with other 1 1 people/set, * * * 1? 12= 132 (disk), but when calculating the total number of disks, the number of' participating disks' of each person is counted again (for example, A? A game of b, b? A counted another set), so the actual match is 132? 2=66 (disk).
Contaminated pill jar
Math brain teaser: There are four jars filled with pills, and each pill has a certain weight. The contaminated pill is the unpolluted weight+1. Only once, how can you tell which jar is polluted?
Answer: Take1for the first medicine bottle; Take out 2 pills from the second medicine bottle; Take out 3 bottles from the third medicine bottle; Take 4 from the fourth medicine bottle;
Calculate the weight of standard 10 pills and compare it with current 10 pills.
If the weight is greater than 1, the first bottle is polluted.
If the weight is greater than 2, the second vial is contaminated.
If the weight is greater than 3, the third bottle is contaminated.
One second before the collision
Math brain teaser: the distance between two cars 1500m. Suppose the front car is driving at a speed of 90km/h and the rear car is rear-ending at a speed of144km/h. What is the distance between the two cars one second before the collision?
Answer: Distance15m.
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