These are independent events but the prob is given for atleast.how to do this?

Hello Student

We have, Number of students failed in Physics = atleast70%
Number of students failed in Chemistry = atleast72%
Number of students failed in Mathematics = atleast80%
Number of students failed in English = atleast85%
⇒Number of students passed in Physics = atmost30%
Number of students passed in Chemistry = atmost28%
Number of students passed in Mathematics = atmost20%
Number of students passed in English = atmost15%
So,the number of students passed in all subjects = atmost(30+28+20+15)%
=atmost 93%
Hence, the number of students failed in all the four subjects = atleast(100−93)% = atleast7%.

I hope this answer will help you.