600 students took test on Physics and chemistry. 35% students failed in Physics and 45% students failed in chemistry and 40% of those who passed in chemistry also passed in Physics, n how many students failed in both :

Result	Physics	Chemistry
Failed	35%	45%
Passed	65%	55%

Now, 55% of 600 passed in Chemistry = $$\frac{{55 \times 600}}{{100}}$$   = 330
From question, 40% of those who passed in Chemistry(330 Students) also passed in physics
= $$\frac{{40 \times 330}}{{100}}$$
= 132,
so, 132 students passed in both
Therefore % who passed in both = $$\frac{{132 \times 100}}{{600}} = 22\% $$
Passed in both subject = 22% of total students
% of students who passed in either Physics or Chemistry or both,
= (65 + 55) - 22
= 98%
Thus, percentage of students who failed in both subjects = 2%
Number of students who failed = 2% of 600 = 12