Six kinds. Suppose that two kinds of story books are story one and story two, and three kinds of science and technology books are science and technology one, science and technology two and science and technology three, then all possibilities are: story one, science and technology one; Story 1, technology 2; Story 1, technology 3; Story 2, Technology1; Story 2, technology 2; Story 2, technology 3.

Xiaohua can choose a story book first. There are two possibilities:

1. Choose a story 1. After that, Xiaohua needs to choose one of the three science and technology books, namely: story 1, science and technology1; Story 1, technology 2; Story 1, technology 3.

2. Choose Story 2, and then Xiaohua needs to choose one of the three science and technology books, namely: Story 2, Science and Technology1; Story 2, technology 2; Story 2, technology 3.

Extended data:

Basic counting principle and application of two commonly used arrays

1, addition principle sum classification counting method;

Each method in each class can accomplish this task independently; The specific methods in the two different methods are different from each other (that is, the classification is not heavy); Any method to accomplish this task belongs to a certain category (that is, classification does not leak).

2. Multiplication principle and step counting method:

One method of any step can't complete this task, and only by continuously completing these n steps can this task be completed; Each step is independent of each other; As long as the methods used in a step are different, the corresponding methods to complete it are also different.

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