In a college, 40% students attend mathematics class,30% students attend physics class and 20% students attend both classes. If a student is chosen at Random from the college, the probability that the students chosen attend only one class is.

Let P(A) be the probability who attend maths class and P(B) be the probability who attend physics class
P(A)=40% , P(B)=30%
Probability of student who attend only maths class= $P\left(A\right)-P(A\cap B)$
$=40\%-20\%=20\%$
$\therefore$ Probability of student who attend only physics class=30%-20%=10%
$\therefore$ Probability that the student chosen attend only one class=20%+10%=30%
$\therefore \frac{30}{100}=\frac{3}{10}$