Combine the following pair of statements using “if and only if”.
p : If the diagonals of a quadrilateral bisect each other, then it is a parallelogram.
q : If a quadrilateral is a parallelogram, then its diagonals bisect each other.

Write each of the statements in the form “if p, then q”.
(i) p :  It is necessary to have a password to log on to the server.
(ii) q : There is a traffic jam whenever it rains.
(iii) r : You can access the website only if you pay a subscription fee. 

Write the following statement in five different ways conveying the same meaning.
“If a number is a multiple of 9, then it is a multiple of 3.”

Write the converse and contrapositive of following statements:
(i) If you live in Delhi, then you have winter clothes.
(ii) If a quadrilateral is a parallelogram, then its diagonals bisect each other.

Write the converse of the following statements :
(i) If a number n is even, then n² is even.
(ii) If you do all the exercises in the book, you get an A grade in die class.
(iii) If two integers a and b are such that a > b, then a - b is always a positive integer.

For each of the following compound statements, first identify the corresponding component statements. Then check whether the statements are true or not.
(i) If a triangle ABC is equilateral, then it is isosceles.
(ii) If a and b are integers, then ab is a rational number.