Four students P, Q, R and S are shown a box which contains a few white balls, and a few red balls. Their teacher asks each of them individually to make a statement. The teacher knows that exactly one of them is a liar and others are not. From the statements that they make, the teacher is able to find out who the liar is. Given below are the statements made by the students. Who is the liar? P says: There are equal number of red balls and white balls. Q says: P is a liar and there are 3 red balls and 2 white balls. R says: Q is not a liar and there are some red balls and some white balls in the box. S says: R is not a liar.