The first volume of the fourth grade is a 40-word encyclopedia of mathematical stories.

1. A farmer invited engineers, physicists and mathematicians to enclose the largest area with the least fences.

The engineer fenced a circle and declared that it was the best design.

The physicist stretched the fence into a long straight line. Assuming that the fence is infinitely long, they think it is big enough to surround half the world.

The mathematician gave them a big laugh.

He surrounded himself with several fences and then said, "I'm outside now."

Thales saw that people were reading the notice, so he went to check it. The original notice said that Pharaoh wanted to find the smartest person in the world to measure the height of the pyramid, so he went to Pharaoh, and Pharaoh asked Thales what tools to use to measure the pyramid.

Thales said he only used a stick and a ruler. He put the stick next to the pyramid. When the shadow of the stick was as long as the stick, he measured the length of the shadow of the pyramid and half the length of the bottom of the pyramid. Add these two lengths to get the height of the pyramid. Thales is really the smartest man in the world. He can easily measure the height of the pyramid without climbing to the top.

3. During the Warring States Period, Qi Weiwang and Tian Ji raced, and Qi Weiwang and Tian Ji each had three good horses: getting on, winning and dismounting.

The race is divided into three times, and thousands of dollars are bet on each horse race. Because the horsepower of the two horses is almost the same, and Qi Weiwang's horse is better than Tian Ji's, most people think that Tian Ji will lose.

However, Tian Ji took the advice of his disciple Sun Bin (a famous strategist) and dismounted Qi Weiwang's horse, Ma Zhong of Qi Weiwang and Qi Weiwang. As a result, Tian Ji beat Qi Weiwang 2-/kloc-0-and won a lot of money. This is an example of China's ancient substitution game theory to solve problems.

A snail accidentally fell into a dry well. It lay at the bottom of the well and began to cry. A toad crawled over and whispered to the snail, "don't cry, little brother!" It's no use crying. The shaft wall is too high. If you fall here, you can only live here.

I have been here for many years, and I haven't seen the sun for a long time, let alone want to eat swan meat! The snail looked at the old and ugly toad and thought, "What a beautiful world outside the well! I can never live in a dark and cold well like it! "

The snail said to the toad, "Uncle toad, I can't live here. I must climb up! " How deep is this well? ""Ha ha ha ..., are you kidding! The depth of this well is10m. How can you climb up with such a heavy shell at a young age? " "I am not afraid of suffering, not afraid of being tired. I always climb out after a while every day! "

The next day, the snail ate and drank enough and began to climb the wall. It kept climbing and finally climbed 5 meters at night. The snail was very happy and thought, "At this rate, I can climb up tomorrow night." Thinking about it, it fell asleep unconsciously. In the morning, the snail was awakened by a purr.

At first glance, it turns out that uncle epilepsy is still sleeping. It was surprised: "How come I am so close to the bottom of the well?" It turned out that this snail slipped 4 meters from the borehole wall after falling asleep. The snail sighed, gritted his teeth and began to climb again.

At night, it climbed another 5 meters, but at night the snail slipped another 4 meters. Climb and climb, and finally the strong snail climbed up the well platform. Can you guess how many days it will take a snail to climb the drilling platform?

One day, a butterfly flew around among the flowers in the animal city, and a little dragonfly flew over and said, Little dragonfly, let's play together. The little butterfly says, I am a butterfly and you are a dragonfly. How can we play together?

Dragonfly said: In the graphic kingdom, we are a family with many family members. Do not believe me, I will show you .. On the way, the butterfly saw many beautiful scenery and many animals: beautiful peacocks, cicadas, ladybugs ... Children, are they beautiful? What do you think is beautiful about them?