The demonstration of things is combined with the line drawing to explain to the children and understand the meaning of walking opposite: walking face to face; Understanding meeting: being in the same place; Understand that starting and meeting at the same time: the time spent by each other is the same; Understanding: the distance traveled by A = speed × time, and the distance traveled by B = speed × time; Understanding: distance traveled by A+distance traveled by B = whole journey.

Use this idea to calculate first: 60×4+40×4=400 (km). Let the children talk about the meaning of each step of calculation: what is 60×4? What is 40×4? What is the sum of the two products?

Then you can guide your child to try to list the formula of (60+40)×4 with the law of multiplicative association.

If the child can't learn yet, he can be guided in this way. 1 hour How many kilometers did the two cars walk? Answer: (60+40) kilometers. So how many (60+40) kilometers is a four-hour drive? Answer: 4. Then we can get the formula of (60+40)×4. Let the children work out the results and see if they are the same.

Then ask the child: which method is simpler?

Finally understand the meaning of (60+40)×4: What is (60+40)? (1 hour distance traveled by two cars), tell children: Add the two speeds together and we call it "speed sum"; What does 4 in the formula mean? The time from departure to meeting, referred to as meeting time. So we come to the conclusion that distance = speed × meeting time.

This calculation formula.

After understanding this formula, it is not difficult to solve the application problem by using the benefit equation. Generally speaking, you can set what you want as X and apply publicity.

take for example

Find the meeting time: (speed sum) ×X= distance.

Find a speed: (X+ b speed) × meeting time = distance.

And so on.