Q: Philip says truth only one day in a week.

Hint 1: Days are Sun, Mon and so on.
Hint 2: One day he says "I lie on Mon and Tue".
Hint 3: Next day he says "Today is either Thu, Sat or Sun".
Hint 4: Next day he says "I lie on Wed and Fri".

On which day he says the truth?

Answer :

Pulkit
Its tuesday.

Hint 2 and Hint 3 are LIES, and Hint 4 is TRUE.
We know from above that on third day, he must have spoken on a Tuesday, Wed, Thurs, or Sat.
The only day which allows this to fit with the converse of Day One (I tell the truth on Monday or Tuesday) is TUESDAY.