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