Introductory Physics question in Forces and Works chap.

[KT KIM]

First of all, I am not from English-using country so excuse my short english skill.

This is the question from Halliday. I have solved this problem and checked the answer from my reference
which started its statement with below

F + Fn − (m + M)g = (m + M)a
where m = 0.250 kg is the mass of the cheese, M = 900 kg is the mass of the elevator cab,
F is the force from the cable, and 3.00 N, Fn = is the normal force on the cheese.

And I think this explanation is wrong
Shouldn't it be F - (m+M)g = (m+M)a ?
Cuz what I think is
for elevator) F-Mg-Fn=Ma (i)
for cheese ) Fn-mg=ma (ii)
(i)+(ii) -> F - (m+M)g = (m+M)a

If I am wrong, please tell me what is my error.

 

[Chestermiller]

You're right and your reference is wrong.

Chet

 

[KT KIM]

Thank you for your help!