120 students appeared for 4 subject tests in a Science Olympiad. Out of them, 95 passed in Physics, 91 in Chemistry, 92 in Biology, and 88 in Maths. What is the maximum number of people who could have passed in all 4 tests, given that every student passed in at least 1 subject?

the answer is 81
this is how i got

let A=number of studs who passed in 1 subject
B= No of Studs in 2 subjects
C= No of studs in 3 subj
D= No of Studs in 4 subjects

Now A+B+C+D = 120 (total no of students)
A+2B+3C+4D= 95+92+91+88 = 366
Subtracting eqn2 from eqn1
B+2C+3D=246
Since B and C are atleast 1
So we get 3D=243
So D=81

82, use chocolate distribution method.

82

82

82

88?