Many GMAT questions are fixed and will appear in every exam, such as the probability questions in GMAT mathematics. This kind of question type is easy for many students who are proficient in or have mastered the problem-solving method, and it is given separately, but many people have no concept of probability. The following GMAT test skills introduce how to deal with probability problems.

There are formulas about the types of sets, such as what AUBUC equals, many patterns and complicated memory, so Webster's diagram must be drawn. Knowing this formula, you can deduce it yourself. For example, what is AUBUC equal to? Draw a picture:

AUBUC= three pieces add up, but you will find that orange, green and purple are added twice each, and then subtracted again; After the subtraction, subtract the black place in the middle and add it back, which is the formula: P (A U B U C) = P (A)+P (B)+P (C)-P (AB)-P (AC)-P (BC)+P (ABC).

It is very convenient to use Wayne diagram for such messy things as "how much belongs to A and how much belongs to B, how many people have A and B, and how many people have nothing".

The second difficulty of GMAT mathematical probability problem is permutation and combination.

When to use permutation, when to use combination and when to use exponential form? This involves the test skills of GMAT. If the last selection has nothing to do with the previous selection, the index is used. For example, five people in a room ask when they were born. There are several possibilities. What day was A born? It has nothing to do with some people in B, C and D. You gave birth to you and I gave birth to me. Seven days a week, so all the possibilities are 7/5. The problem of permutation and combination is often taken out the first time and disappeared the second time. For example, if you choose three out of twelve people, the first person will slap me, and when you choose the second person, I will be gone. Exponential form is suitable for "not putting back", and permutation and combination are used for "putting back"

When will the GMAT test be arranged and combined? Arrange what can be distinguished and combine what can't be distinguished. For example, choose three out of eight people to go abroad and ask how many possibilities there are. If you choose to go abroad, there is no difference, that is, three out of eight, C38. How many possibilities are there for three out of eight people to go to Laos, Vietnam and Cambodia respectively? Laos, Vietnam and Cambodia are abstract numbers of three places, indicating that the three places are different and should be arranged after being drawn out. I go to Laos and you go to Vietnam, which is different from me going to Vietnam and you going to Cambodia. So arrange, P38.