**IBDP** **Mathematics**** Question Analysis Topic: Mathematics - Probability**

**Exam Question:**

Of the students in a school, it is known that 30% have 100% attendance and 70% students are irregular. Previous year results report that 70% of all students who have 100% attendance attain A grade and 10% irregular students attain A grade in their annual examination. At the end of the year, one student is chosen at random from the school and he was found to have an A grade. What is the probability that the student has 100% attendance? Is regularity required only in school? Justify your answer.

**Answer:**

For IBDP Mathematics, you should know:

If **70%** of students are **irregular **and **30%** are in **full attendance**, then let** a = 0.3 be the chance of full attendance.**

Let** b = 0.7 be the chance of irregular attendance**.

Given that 10 percent of students with irregular attendance earn grades of A, and also 70% of students with 100% attendance do:

The odds of a pupil being picked up with an A are 0.7 x 0.3 + 0.7 x 0.1 = 0.21 + 0.07 = 0.28.

The chosen student's likelihood of having perfect attendance will be 0.21/0.28 = 3/4.

No, regularity is necessary in all facets of our lives.

Work hard for your IBDP Mathematics examination!

End of analysis. Great!