How many students failed?

• The number of students who only passed in math is $88-70 = 18$

• The number of students who only passed in physics is $80-70 = 10$

So $10+18+70 = 98$ . Hence $100 - 98 =\boxed{2}$ students failed in both subjects.

Let the set of the students who passed in maths be $M$ .

Let the set of the students who passed in physics be $P$ .

So, the students who passed in both subjects are in $M \cap P$ .

The students who passed in math only = n (M) - n (M \cap P) = 88 - 70 = \color \red{18}

The students who passed in physics only = n (P) - n (M \cap P) = 80 - 70 = \color \red{10}

So, the students who passed in at least one subject are = \color \red {18+10+70 }= \color \red { 98}

Therefore, the students who could not even pass in one subject are = \color \red{100} - \color \red {98} = \boxed {\color \red {2}}.

Answer
= 100 + 70 - 88 - 80
= 2