Question

​a sealed envelope contains a card with a single digit on it.three of the following statements are true and one is false.
1.the digit is 1
2.the digit is not 2
3.the digit is not 9
4.the digit is 8

Answer 1

2. one is true & rest are false.

Answer 2

By given information we can only know that EITHER ONE OF statement 1 and 4 is false.
But we can be sure that both statement 2 and 3 are true.