1, the problem of chickens and rabbits in the same cage: suppose they are all chickens and rabbits. How many feet are there? How many feet are missing? Divided by the foot difference, it is the number of chickens and rabbits.

2. Concentration problem: sugar should be added before adding water, and sugar water should be added after sugar. Sugar water plus sugar water is the amount of water added.

3, catch up with the problem: the slow bird must fly first, and the fast bird will catch up later. Divide the distance you go first by the speed difference, and the time is right.

4, there is still a problem: the family wants everyone to be together, and there are principles for separation. Denominator ratio sum, numerator's own. And multiply by the ratio, you deserve it.