Analysis: The key to solving this problem is that it is not difficult to get the answer by using the method of reverse deduction according to the meaning of the problem. A caterpillar grows from a larva to an adult, doubling its size every day and growing to 20 cm in 30 days. It is inferred that it will take 29 days to 10 cm, and 28 days to 5 cm, from which the answer can be obtained.
The problem solving process is as follows:
Solution:
30- 1- 1
=29- 1
=28 days
A: It takes 28 days to grow to 5 cm.
When solving the formula of application problems by inverse deduction, it is often necessary to subtract the addition and subtraction operations, and add them according to the relationship between addition and subtraction operations and multiplication and division operations. Divide the multiplication in the original problem by the multiplication.
Mathematical problems suitable for reverse deduction should have the following characteristics:
1, and the final result is known.
2. The process (each step) of reaching the final result is clear; (that is, the change process is clear)
3. Need the original situation.