Keywords: interesting doctor, grade two, primary school
This article is applicable to: the second grade of primary school.
Composition source:
This 400-word composition is about the second grade of primary school. The title is "Doctor of Mathematics-Interesting Story of Iron Egg (1)". Everyone is welcome to contribute enthusiastically.
Doctor of Mathematics-Interesting Story of Iron Egg 1
-continue to write the adventures of a desert island.
Tie Dan is a clever little boy who treats people warmly, but he doesn't like to pay attention in class. So he didn't study much, especially math. One day, Iron Egg walked dejectedly with a 59-point math paper. I met a clever puppet troupe and went to see a puppet show together, and I got lost. That's right. I met the fat president. In the battle between the dwarf country and the long country, he helped the dwarf country popularize mathematical knowledge, repelled the attack of the long country, and won the title of doctor of mathematics. When I went back to school this time, the news was like a frying pan, which suddenly boiled up, and everyone set off a craze for learning mathematics.
On the way to school, he saw his cousin and a fat boy in grade three quarreling, blushing like a bee. Iron egg quickly stepped forward and grabbed his cousin and asked them why they quarreled.
The fat boy said angrily, "Today, the teacher asked the group leader to approve the math homework. I did the problem correctly, but he gave me a big "X". He just retaliated against the last time I told the teacher that he took the card to school. "
"You wronged someone, obviously you did something wrong, and you said I wanted to get back at you." My cousin said angrily.
"Stop, stop, stop," said Iron Egg. "Let me see what it is."
Xiaohong does bicycle practice, riding from place A to place B at a speed of 30 kilometers per hour; Ride from B to A at 20 kilometers per hour. What is Xiaohong's average speed to and from the two places?
"This formula is not (30+20)÷2=25 (km)? What's wrong? " The fat boy said confidently.
"This is obviously the average speed, not the average speed. He also said that I have personal grievances. " My cousin stood aside angrily.
Little classmate, this is where you are wrong. The calculation method of average speed is "total distance ÷ total time". This problem can be assumed that the distance between A and B is 60 kilometers, so the time to ride from A to B is 60÷30=2 (hours), the time to ride from B to A is 60÷20=3 (hours), and the average speed to and from the two places is 60×2÷(2+3)= 1
"Sorry, I was wrong." The little boy hung his head shyly. A pair of good friends went home happily hand in hand.
Iron egg told the students to remember that the average speed is not the average speed, so don't average it casually!