21. Price increases then demand falls.
p → q
22. If price does not increase then demand does not
fall.
~p → ~q
23. Price increases if and only if the demand falls.
p ↔ q
24. If the diagonals of a parallelogram are
perpendicular then it is a rhombus.
p → q
25. If the parallelogram is not a rhombus then
diagonals of it are not perpendicular.
~p → ~q
26. If the diagonals of a parallelogram are not
perpendicular then it is not a rhombus.
~p → ~q
27. Mango is a fruit but potato is a vegetable.
p ˄ q
28. Either we play football or go for walking.
p ˅ q
29. An angle is a right angle if and only if it is
of measure 900.
p ↔ q
30. 14 is a composite number and 15 is a prime number.
p ˄ q