Asingle die is rolled. find the probability of rolling an even number or a number less than 6.

Single die can give us 6 values: {1,2,3,4,5,6} so the collection of possibilities has 6 numbers. In the event A there is even number or number smaller than 6, so there are even numbers {2,4,6} of number smaller than 6 {1,2,3,4,5}.
Probability will be equal to 1, because the whole event collection contains every possibility.

In rolling a die, the probability of obtaining an even number is 3/6 or 1/2 as there are 3 even numbers. Further, the probability of obtaining a number less than 6 is 5/6. The common entities between these two events are obtaining 2 and 4, with a probability of 2/6 or 1/3. The final probability is therefore,
                              3/6 + 5/6 - 2/6 = 1
Thus, the probability is 1. 

The answer is option c.